WO2002027720A1

WO2002027720A1 - Method of manufacturing and authenticating a card printed with digital information by digital watermarking technique and its apparatus therefor

Info

Publication number: WO2002027720A1
Application number: PCT/KR2001/001620
Authority: WO
Inventors: Jong-Uk Choi; Jung-Su Lee; Won-Ha Lee
Original assignee: Markany Inc.
Priority date: 2000-09-26
Filing date: 2001-09-26
Publication date: 2002-04-04
Also published as: JP3712392B2; JP2004510277A; KR20010087749A; KR100373443B1; AU2001292414A1

Abstract

For producing the card printed with digital information, a digital image to be printed on the card is manufactured by using information provided by an applicant who requests the issuance of a card, or information on issuance extracted from a database with the information on authentication. At the same time, a watermark is generated by using the information on authentication, the watermark is embedded into the digital image and then, the water-embedded digital image is printed on the card. Thereafter, a watermark-embedded region is captured from the digital image generated by scaning the printed image, and a watermark is extracted from the digital image within the watermarking-embbeded region, Meanwhile, a watermark is generated by inputting information on authentication obtained from a cardholder. Then, the authentication is determined from the co-relation between the extracted watermark and the generated watermark.

Description

METHOD OF MANUFACTURING AND AUTHENTICATING A CARD

PRINTED WITH DIGITAL INFORMATION BY DIGITAL WATERMARKING TECHINIQUE AND ITS APPARATUS THEREFOR

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a method and apparatus for producing and authenticating a card with digital information printed using a digital watermarking technique, more particularly, to a method and apparatus for producing and authenticating a card with digital information printed by forming the content to be printed as digital information and embedding a watermark indistinguishable with the naked eye in producing a card with information printed.

Description of the Related Art

ID cards such as identification card, passport, student identification card, employee card and the like and various cards such as driver's license, qualification card, credit card, card key and so on which include identity information or prove/ascertain identity have been widely used long ago in order to prove one's identity or qualification. In spite of the importance of information contained in such cards, illegal forgery/alternation of a card has been on the increase.

The following methods have been employed to solve such problem: First, there is a method of attaching and coating a picture to the printing paper with identity information printed. Such method is employed in a passport at present. However, if the picture of a card is just identical to the cardholder, since the card and the cardholder are all authenticated, such method has a problem that the card is easily modified by removing a coating and replacing pictures and finishing the card properly.

Second, there is a barcode method that is a code system indicating information as the arrangement pattern of black bar and white bar having various widths. An ID card that is produced by attaching or printing a barcode thereon ascertains the authenticity of the ID card, identity information and the cardholder based on information read from a barcode reader when a person enters and goes out. However, it is possible to imitate a barcode having the same pattern and use it illegally due to its easy photocopy. Further, a simple modification of the pattern results in a quite different material for authentication, which causes a high possibility of forgery/alternation. In addition, since a barcode reader frequently fails to read a barcode, a keyboard should be prepared for such case.

Third, there is a magnetic line in which a predetermined information is recorded in a magnetic manner. Most of credit cards select a method of attaching a magnetic line on the back of the card and recording information in the magnetic line and providing the minimum information regarding the corresponding credit card. However, such method has problems that contact with a material having strong magnetism causes damage in the information recorded in a magnetic line and easy reading of information recorded in a magnetic line makes its imitation and modification easy.

Meanwhile, there are two methods for discriminating the authenticity of a cardholder wherein one is to discriminate it with the naked eye through a picture and another is to discriminate it using a password. However, a method using a picture, as described above, is not only useless under the circumstance where forgery/alternation is easy but also restricted by time in comparing the cardholder with the picture attached or printed on the card one by one and thus falls behind in its discrimination. The method of comparing the password of the cardholder with her/his actual password is most widely used at present. However, a password consists of generally an Arabian number of four figures and thus it is easy for a person having unlawful intention to figure out the password. A frequent change of password makes it possible to maintain its security from the third party. In this regard, however, going through formalities of change in a password or making up and remembering a new password are disadvantageously very cumbersome. Both methods of the discrimination with the naked eye and the password comparison may be employed, however, even simultaneous use of both methods can not clearly solve the above mentioned problems. Lately there is a method of digitalizing information recorded in a card and printing it in order to solve the above problems. However, such digitalization makes it possible to photocopy the original unlimitedly without damage thereof and makes it difficult to discriminate a photocopy from the original, which causes illegal photocopy and illegal circulation. Although aforementioned methods are at present applied to prevent cards from being used illegally by means of its forgery/alternation thereof, they have many problems that it is distinguishable with the naked eye or, the modification is easy due to easy reading of the recorded information or, it is very small amount of information capable of being concealed or, it is easy to be damaged or, it is restricted by time, etc. Such limitations of the conventional art, despite of its importance, cause an illegal use of a card.

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide a method and apparatus for producing and authenticating a card with digital information printed using a digital watermarking technique incapable of forging/altering a card by embedding a watermark indistinguishable with the naked eye into digital image to be printed. It is another object of the present invention to provide a method and apparatus for producing and authenticating a card capable of printing by embedding a watermark while minimizing deterioration in the quality of digital information to be printed on a card.

It is another object of the present invention to provide a method and apparatus for producing and authenticating a card wherein digital information with strong feature and high conservancy of watermark regarding modification in image to be printed on a card is printed while not deteriorating the quality of digital information by embedding a watermark into digital information to be printed using frequency domain feature. In order to achieve the objects as described above, the present invention provides an apparatus for producing a card which contains information for authentication, comprising: means for storing information for issuing a card and information for authenticating a card from a card issuance applicant; means for transforming said information for issuing a card in said means for storing into a digital image having a predetermined size; means for setting said information for authenticating a card in said means for storing to a user key and generating a watermark using said user key; means for embedding said watermark in said digital image; and means for printing a watermark-embedded digital image on the card material.

The present invention provides an apparatus for authenticating a card produced, comprising: means for generating said digital image by scanning said image printed on a card; means for allowing a cardholder to input the information for authenticating a card; and means for determining whether the card to be authenticated by calculating correlation between the watermark generated using the information for authenticating a card inputted by a cardholder and the watermark extracted from said digital image.

Methods used in the above apparatus can be constituted in the same form. In producing a card as described above, embedding a watermark indistinguishable with the naked eye allows for making its modification difficult. Further, if a watermark is generated in accordance with a key determined by the genuine cardholder, when authenticating a card or discriminating the authenticity of the cardholder, modification/change of the card or the authenticity of the cardholder is determined based on the comparison between the watermark extracted from a card and the key inputted from the cardholder. Further, it can make the content of information to be concealed various, optionally select where to locate information to be concealed, and there is no concern that a watermark itself could be damaged and its modification is difficult as well. Additionally, the extraction and comparison of a watermark using a computer make it possible to facilitate an accurate examination. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram illustrating schematically the constitution of a card producing apparatus for producing a card containing a digital watermark according to an embodiment of the present invention.

Fig. 2 is a flow chart illustrating a process of producing a watermarked card according to the card producing apparatus referring to Fig. 1.

Fig. 3 is a detailed block diagram illustrating specifically the watermark- related constitution referring to Fig. 1. Fig. 4 is a flow chart illustrating a process of producing a watermark- embedded digital image according to the constitution referring to Fig. 3.

Fig. 5 is a block diagram illustrating the constitution of a card authentication apparatus for authenticating a card produced by the card producing apparatus referring to Fig. 1. Fig. 6 is a flow chart illustrating a process of authenticating a card in the card authentication apparatus referring to Fig. 5.

Fig. 7 is a detailed block diagram illustrating specifically the constitution of a watermark authentication server referring to Fig. 5.

Fig. 8 is a flow chart illustrating a process of comparing a watermark of a card according to the constitution referring to Fig. 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinbelow a method and apparatus for producing and authenticating a card with digital information printed using a digital watermarking technique according to the present invention referring to the figures attached are explained in detail.

In general, a process of issuing a card is as follows: A person who requests to issue a card provides a card producer/issuer with information necessary for issuing a card such as his/her personal information (e.g., name, identification number, address, bank account, etc.) or picture. At this time, a person who requests to issue a card designates the key value to provide a card producer/issuer with it. The key is information of characters or numbers like password, employee number, or various IDs, etc. A card producer/issuer stores information provided from the person who requests to issue a card including a key in a database and extracts only the information to be printed on a card material from the database among the information provided from the person who requests to issue a card. Thereafter, using a general graphic tool for producing a card, a digital image that is extracted from the database and includes information to be printed on the card material is produced. As producing a card finishes when the digital image produced using a general printer for producing a card is printed on the card material, the card is issued to the person who requests to issue a card.

The present invention, in a process of producing the aforementioned card, generates a watermark using a key provided from a person who requests to issue a card and then further comprises a process of embedding the watermark into the digital image to be printed on the card material so that concealing a key makes imitation or photocopy difficult, thereby preventing a card from being forged/altered. Further, it can authenticate a card or discriminate the authenticity of a cardholder by detecting the concealed key and examining whether the key is identical to a key inputted by the cardholder through an outer inputting apparatus. Hereinbelow the constitution of the present invention is explained in detail referring to the figures attached.

Fig. 1 is a block diagram illustrating schematically the constitution of a card producing apparatus for producing a card including a digital watermark according to an embodiment of the present invention. The card producing apparatus 10 of Fig. 1 comprises card information database 20 for containing information necessary for issuing a card, digital image generator 30 for realizing the digital image using the card information, watermark generator 40 for generating a watermark in accordance with the value of a user key, watermark embedding unit 50 for embedding the generated watermark into the digital image, and digital image printing unit 60 for printing the watermark-embedded digital image on the card.

Hereinbelow, a process of producing a watermarked card according to the above card producing apparatus is explained referring to the flow chart of Fig. 2.

The key value and information necessary for issuing cards of persons who request to issue a card and data related to various uses of card, etc. is stored in the card information database 20 and the key value determined for issuing a card of the corresponding person and information to be printed on the card is extracted (Step S100). A basic digital image to be printed on the card material Such extracted data is produced with such extracted data produce from the information extracted from the card information database 20 by using a graphic tool for producing a card. The graphic tool sets up a predetermined region considering the size of the card to be printed and draws various kinds of materials on the location already set up and makes one data file (Step S110).

Further, the watermark generator 40 generates a watermark by using the user key extracted from the card information database 20 (Step S120) and embeds the generated watermark into the digital image (Step S130). The watermark generated by the watermark generator 40 is embedded into the digital image by the watermark embedding unit 50 (Step S130). Finally, as the watermarked digital image is printed on the card material, producing a watermarked card is completed (Step S140). In particular, the present invention applies a new method different from the conventional method for generating and embedding a watermark to be embedded into the card, which is explained referring to Fig. 3 and Fig. 4.

Fig. 3 is a detailed block diagram illustrating specifically the watermark- related constitution referring to Fig. 1 and Fig. 4 is a flow chart illustrating a process of producing a watermark-embedded digital image according to the constitution referring to Fig. 3.

Fig. 3 illustrates the detailed constitution of the watermark generator 40 and watermark embedding unit 50. In this connection, the watermark generator 40 comprises user key encrypting unit 41 for encrypting the user key inputted from the card information database 20 and pseudo random number generator 42 for generating a pseudo random number from the encrypted user key. The watermark embedding unit 50 comprises a gray image/color image discriminator 100 for discriminating whether the inputted digital image is a gray or color, a color model transformer 110 for transforming a color model for easily dealing with the image in case where the corresponding inputted image is a color, a frequency domain transformer 120 for transforming the inputted signal from the spatial domain to the frequency domain, a watermark embedding unit 130 for embedding a watermark generated in the watermark generator 40 into the digital image which is transformed to the frequency domain, an inverse frequency domain transformer 140 for transforming the watermark-embedded digital image from the frequency domain to the spatial domain, and an inverse color model transformer 150 for transforming the transformed color model into the original color model in case where the transformed signal is a color model.

The movements of the watermark generator 40 and watermark embedding unit 50 having the above constitution are, by steps, explained referring to Fig. 4.

The digital image generated in^' the digital image generator 30 is inputted in the watermark embedding unit 50 (Step S200). The inputted digital image is inputted in the gray image/color image discriminator 100 which discriminates whether the digital image into which a watermark will be embedded is a gray image or color image (Step S210). The gray image / color image discriminator 100 extracts image information data relating to the format of the inputted digital image to discriminate whether the inputted digital data is a gray image or color image on the extracted image information data.

As a result of discrimination by the gray image / color image discriminator 100, in case where the corresponding digital image is gray, it is transformed to the frequency domain by the frequency domain transformer 120 (Step S22U_!). At this time, since a gray image has only the component of luminance, an immediate transformation from the spatial domain to the frequency domain is executed by the frequency domain transformer 120.

Differently from this, in case where the result of discrimination by the gray image/color image discriminator 100 is a color image, in the color model transformer

110, it is transformed from the color model like RGB mode, etc. to the color model of HSB (H:hue, S saturation, B:brightness) mode, YIQ (Y:luminance, I:in-phase, Q:quadrature) mode or YcbCr (Y:luminance, Cb/Cr: chrominance) mode, and the component of luminance of the transformed color model is extracted (Step S215). The component of luminance of the color model transformed by the color model transformer 110 is transformed to the frequency domain by the frequency domain transformer 120 (Step S220₂). There are many methods for transforming a digital image to the frequency domain wherein FFT (Fast Fourier Transform), DCT (Discrete Cosine Transform), DWT (Discrete Wavelet Transform), etc. may be representatively employed. The present invention employs a frequency domain method for embedding and extracting a watermark. That is why the transforms by the frequency domain method have advantages that they make removal of watermark difficult by concealing a watermark in the digital image and do not largely deteriorate quality of the original digital image. According to the frequency domain transformer 120, DCT coefficient, FFT coefficient, or DWT coefficient (FOI) of the digital image is obtained.

Meanwhile, it is difficult to embed the watermark information into Fourier transform coefficient since in Fourier transform coefficients of the transform domain comprise complex numbers, whereas DCT includes a feature similar to Fourier transform, but coefficients of the transform domain comprise real numbers. Hence, DCT is more advantageous and easier than Fourier transform. DCT is basically in a close relation with FFT and is a transform method widely used in the standard JPEG compression, etc.

The first dimensional DCT is defined as in the following equation la:

[Equation la] *< ) = c(Jcy _Λsjri) cos ^

In the above equation la, s is an original signal value, t is a transformed signal value, N shows the length of signal, and the coefficient c is as in the following equation lb:

[Equation lb]

(Only, in case of 1 ≤k≤N-1)

On the other hand, the second dimensional DCT regarding a square matrix is defined as in the following equation 2a:

[Equation 2a]

In the above equation 2a, N, s, and t have the same meaning as in the first dimensional DCT, c(i, j) is as in the following equation 2b:

[Equation 2b] c(0_> j) = l /N₉ c(i,0) = l/ΛT _? c(i₉ J) = 2/N

(Only, in case of i≠O, j≠O)

Further, the DCT has an inverse transform and is defined as the following equations 3a and 3b regarding each of the first and second dimensions:

[Equation 3a]

[Equation 3b]

Next, the DWT is reviewed. Fourier transform employs a sine function and cosine function as its basis function, whereas Wavelet transform uses wavelet as its basis function, which is divided into a continuous wavelet transform and discrete wavelet transform. The continuous wavelet transform is defined as in the following equation 4.

[Equation 4]

In the above equation 4, s indicates scaling, τ indicates translation, ψ (s, t) indicates wavelet which is scaled and translated. The scaling is related to a frequency. A low scaling, i.e., the compressed wavelet extracts a high frequency component and a high scaling, i.e. the extended wavelet extracts a low frequency component. Usually, it is impossible to virtually realize the continuous wavelet transform since the wavelet coefficients obtained from the transform are infinite as a function of scaling and translation.

Hence, use of the discrete wavelet transform that selects only a certain frequency domain regarding the scaling and translation results in a more effective realization. However, since the discrete wavelet transform also stands a lot of computing amount being realized by a computer, it is desirable to transform the image by using a filter bank, a high-speed wavelet transform. This method uses the conventional two channels of a sub-band coding and a pyramid algorithm and has advantage that it can be easily realized only if the relation (PR-QMF: Perfectly reconstruction quadrature mirror filter) between filter banks for an inverse transform is carried, out.

A predetermined user key from the card information database 20 is inputted in the watermark generator 40 that generates a watermark from the user key. Should the user key is adopted as the watermark, the authenticity o any change of the digital image will be accurately determined based on the correlation between the extracted watermark and the watermark generated from the user key, which advantageously strengthens the security of the watermark.

Furthermore, the corresponding user key is encrypted using the user key encrypting unit 41 before pseudo random number is generated which is used as a watermark from the user key and the encrypted key is inputted and pseudo random number is generated by the pseudo random number generator 42. If the user key undergoes the encryption process, not only the value of the user key will not be easily changed but also the user key itself can be concealed. Thus, when the watermark generated from the encrypted user key is embedded in the digital image, there is advantageously no concern that the user key itself will be revealed when extracting the watermark from the digital image afterwards. The encryption may employ the conventional encryption methods, for example, DES (data encryption standard) method, RSA method, ECC method, etc. The present invention employs a PN- code method that outputs the result of the coded data that will be encrypted in a pseudo random number.

The watermark generated as above is embedded in the digital image by the watermark embedding unit 130 via a process such as the following equation 5 (Step 230_x or Step 230₂).

[Equation 5]

wherein, p is a characteristic function for controlling the intensity of the watermark that will be embedded in the digital image, fk may be variously set up which may be a function either performing a modulo calculation of a portion of the frequency domain transform coefficient (FOI) of the digital image or rendering statistical characteristic values of multiple transforming coefficients such as the mean, standard deviation, and variance, etc.

FOI' represents the result of multiplying the watermark (W) to a value applying characteristic function fx to the frequency domain transforming coefficient (FOI) of the digital image. The transforming coefficient (FOI) in the above equation 5 is a value of the frequency domain of the digital image, therefore is in a two- dimensional arrangement format. The watermark (W) has one dimensional sequence format so that the transforming coefficient (FOI) is transformed into a sequence format or the watermark (W) is transformed into a two dimensional block to perform the calculation. To perform the calculation, there is a method wherein per a frequency coefficient of the image, a watermark is matched thereto to calculate or a method wherein the statistical characteristic of multiple frequency coefficients of the image is selected to perform the calculation with a watermark.

To explain the process of embedding a watermark in more details in reference to Equation 5, the watermark embedding unit 130 performs a process of replacing value obtained as a result of a characteristic function fx applied to a predetermined absolute value of transforming coefficient (hereinafter, referred to as an embedding coefficient) of specific frequency band multiplied by the watermark (FOP, hereinafter, referred to as a replacement coefficient) with other predetermined transforming coefficient of a specific frequency band. For instance, when digital images are divided into low frequency, medium frequency and high frequency band, a watermark is embedded in the medium frequency band or high frequency band wherein relatively small amount of information regarding digital image is included.

Thus, the embedding of a watermark is completed by replacement of a transforming coefficient of the existing medium frequency band or high frequency band with the result of value obtained as a result of a characteristic function fx applied to a transforming coefficient of low frequency band multiplied by watermark (replacement coefficient).

According to such method, even if there is a condensation process removing portion of high frequency parts or transformation such as blurring, the watermark is multiplied to a coefficient of the low frequency band, and replaced with high frequency band. After transformation, a considerable portion of such high frequency band is left. Therefore, there is an advantage of a digital image being strong to transformation.

The present specification discloses replacement of a watermark between medium frequency band and high frequency band by being multiplied to the result of a characteristic function fx applied to an absolute value of a coefficient of low frequency band. Yet, frequency band having a scope of not deteriorating the quality of digital image can be selected, and watermark may be embedded thereto. For example, as it is possible to replace with high frequency band after the watermark is multiplied by the result of a characteristic function applied to an absolute value of a transforming coefficient of high frequency band, a method for embedding a watermark in the digital image transformed to a frequency domain is not restricted thereto, but is applicable to several frequency bands.

Also, if the present invention in observation of the entire characteristics of the image not being changed by printing, by compensating a coefficient of other frequency band with a coefficient of an arbitrary frequency band, uses characteristics of frequency domain which does not make change to the entire characteristics of image, the invention may possess characteristics strong against printing. Thus, disappearance of the watermark due to printing, etc. can be prevented. Furthermore, according to the aforementioned watermark embedding method using characteristics of frequency domain, the entire characteristics of the digital image do not change even at the embedment of the watermark. In other words, the quality of the original digital image is not deteriorated. Thus, it is possible to enjoy the quality of the original digital image even after printing. In Equation 5, the control of the degree of the watermark strength at the embedment of the watermark into the digital image is Function fx. The value of this characteristic function can be set by user's discretion. Thus, any value is feasible, and particularly, an appropriate function which will not deteriorate the quality of digital image due to watermark embedment can be determined. That is, the degree of strength of the watermark and the transformation of the quality of the digital image are in inverse relationship. Thus, it is preferable to make determination in consideration of an environment where the watermark is used and an aspect of maintaining quality of digital image.

Now, in order to acquire watermark-embedded digital image, the inverse frequency domain transformer 140 restores the digital image transformed to frequency domain (S240_j or S240₂). In a case wherein the aforementioned frequency domain transformer 120 uses DCT or DWT or FFT, the inverse frequency domain transformer 140 employs an inverse DCT or inverse DWT or inverse FFT. In this regard, if the digital image is a color image, by inverse color model transformer 150, a restoration to the original color model from the color model of

HSB mode, YIQ mode or YCbCr mode occurs by using the remaining components in exclusion of luminance component wherein the inverse frequency domain transform is performed and of luminance component which did not undergone frequency domain transform (S245). Finally, by obtaining watermark-embedded digital image, process for embedding the watermark into the digital image is completed (S250).

As aforementioned, when watermark-embedding process with regard to digital image is completed, in digital image printing unit 60, the digital image embedded with the watermark is printed on the surface of the card material and then, the watermarked card can be produced.

The position or the content of the watermark embedded in the card which has been embedded with the watermark according to the present invention and produced as such can be determined in variety. Whether the content of the watermark is in characters or numbers or image, or whether the position wherein the watermark is embedded is the entire or partial portion can be determined in variety according to the characteristics of the watermarking method selected by a card producer/issuer. For example, at the aforementioned watermarked card producing stage, if the portion in which the watermark is to be embedded is where the applicant's photograph is, first the designated place where the photograph is to be printed is left empty, and information only to be printed in the card excluding the photograph is printed on the card material. Then, the digital image is generated from the photograph of the applicant for card issuance and the watermark is embedded only to this digital image. Thus, watermark-embedded digital image can be printed on the designated position of the card material. On the other hand, if the portion where the watermark is to be embedded is the entire card, the digital image in the same size as the whole card material is generated from information to be printed on the card. After the watermark is embedded into the digital image, it can be printed out on the card material. Also, if the embedment is to be made into particular portion of the image among which the watermark is to be printed on the card, a method for indicating a particular identifier in the portion where the watermark is embedded may be used.

Apparatus and method for authenticating regarding watermark-embedded card produced through the above generation process is hereinbelow explained in reference to Figs. 5 to 8. A process and apparatus for authenticating a watermarked card is constituted to correspond to the aforementioned card generation process and apparatus thereof. A watermark extraction method used in the process of authenticating a watermarked card corresponds to a watermark embedding method used in the process of generating a watermarked card.

Fig. 5 is a block diagram illustrating the constitution of a card authentication apparatus for authenticating a card produced by the card producing apparatus referring to Fig. 1. The apparatus for authenticating a card 200 of Fig. 5 is largely comprised of a part generating a watermark from the input of a user key and a part processing information recorded in the card itself. So called information recorded in the card itself includes card user information recorded by using the watermark included in the digital information printed on the surface of a card and magnetic strip, etc. The apparatus for authenticating a card 200 may be constituted to link with a database in order for card authenticator to confirm not only the card authentication but also information such as personal identity information or itemized statement of a card. However, an apparatus authenticating only card will not include a separate card information database.

The above apparatus for authenticating a card 200 comprises a card recognition unit 210 for recognizing information contained in the card; a key input unit 220 for inputting user key, etc.; a database search information extracting unit 230 for searching and extracting information regarding the card of the pertinent user by using the extracted data from the card recognition unit 210; a card information database unit 240 for extracting certain information desired by the card authenticator among the above extracted information; a digital image data processing unit 250 for performing a process of extraction, etc. of digital image of the card recognized from the card recognition unit 210, etc.; a watermark authentication server 260 for performing authentication using the extracted digital image and watermark generated from the user key inputted from the key input unit 220; and a result output unit 300 for outputting the result of authentication.

The whole operation process together with the operation of each of the constituent elements of an apparatus for authenticating a card 200 having the above constitution is explained hereinbelow in reference to the flow chart of Fig. 6.

The card authenticator, in order to confirm forgery/alteration of a card and the authenticity of a cardholder, let the cardholder insert the card into the card recognition unit 210 of the watermarked card authentication apparatus, and input key values to the key input unit 220 (S300). The card recognition unit 210 transfers various card information such as card serial number or card user ID, etc. that have been read from the cardholder's inserted card to the database search information extracting unit 230. Meanwhile, the image printed on the card is scanned, and the image printed on the card is formatted in the digital image data. Then, it is transferred to the digital image data processing unit 250.

The database search information extracting unit 230 extracts search information (card serial number or user ID, etc.) for extracting information desired by the card authenticator such as personal identity information of the cardholder or itemized statement of a card, etc. among various card information received from the card recognition unit 210, and transmits to the card information database unit 240. The extraction of search information is achieved from portions recorded in the elements having information record and indication function such as magnetic strip, and bar code, etc. attached to the card. The card information database unit 240 uses search information from the database search information extracting unit 230 to extract information regarding arbitrary card users desired by the card authenticator. The extracted information is transmitted to the result output unit 300, and the process for obtaining card user information is completed (S340 to S360).

Meanwhile, the digital image data processing unit 250 captures images only within the range corresponding to watermark-embedded digital image range at the production of the aforementioned watermarked card, and transmits them to the watermark authentication server 360. The size of the image within the range for capturing is satisfactory if within the size of the card, and is not subject to limitation on size. At this time, in order to extract the watermark from the image printed on the card surface, the position wherein 'the watermark is embedded should be known. In this regard, if the watermark embedding band is determined previously at the watermark embedding process, acquisition of only the image of the position corresponding to such range at extraction of the watermark is adequate. Or, if a separate identifier indicating embedded region at watermark embedment is embedded, such identifier is searched, and then image only within the region determined by such identifier is captured. In order to transmit to watermark authentication server 260 at high speed, watermark-embedded image data can be compressed. The watermark authentication server 260 extracts the watermark from the captured image data (S310). The extraction of the watermark uses an extraction method corresponding to watermarking method applied at embedment. The extracted watermark is compared with watermark generated by the user key (S320), and the result of authentication from the comparison result is outputted in a designated form confirmative by card authenticator. Then, the watermark extraction process and authentication process are completed (S330). The watermark authentication server 260 performing such function comprises the watermark extracting unit 270 for performing extraction of a watermark using transform to the frequency domain and the frequency domain coefficient; a watermark generating unit 290 -for generating the watermark by using the encrypted key after the key inputted by the user has been encrypted; and a comparison operation unit 280 which determines authenticity according to the correlation between the watermark extracted from the watermark extracting unit 270 and watermark generated from the watermark generating unit 290. A watermark extraction method is described hereinbelow in reference to Figs. 7 and 8.

The watermark extraction unit 270 of the watermark authentication server 260 receives watermark-embedded image from the digital image data processing unit 250, and extracts/detects watermark according to the above extraction method of the present invention. If image data is compressed at the digital image data processing unit 250, watermark extraction/detection unit 270 extracts/detects watermark after decompressing the compressed image data in response thereto.

Meanwhile, the cardholder inputs key values in the key input unit 220 of the apparatus for authenticating a card 200. The key input unit 220 transmits key values inputted by the cardholder to the watermark authentication server 260 as digitalized data. The watermark generating unit 290 of the watermark authentication server 260 encrypts the key data received from the key input unit 220 in an identical method with that of the watermark embedment, and generates the watermark using the encrypted key data.

Subsequently, the comparison operation unit 280 determines whether to authenticate from the correlation between watermark extracted from the watermark extracting unit 270 and watermark generated from the watermark generating unit 290, and transmits the authentication result to the result output unit 300. Finally, the result output unit 300 outputs, in a form confirmative by the card authenticator, certain information desired by the card authenticator extracted from the card information database unit 240, and authentication result transmitted from the comparison operation unit 280 of the watermark authentication server 260.

During the above process, when the confirmation as to the card insertion accordmg to the card recognition unit 210 has been made, the watermark extraction and authentication process (S310 ~ S330) for determining card authentication and authenticity of cardholder, and process (S340 ~ S360) for searching and extracting the card user's information from the database required by the card authenticator are respectively carried out. Two processes are independent from each other. Thus, it is desirable to proceed two process in parallel so that the time for such process can be reduced.

Particularly, a process for extracting a watermark related to watermark embedding method used for an apparatus for producing a card of the present invention and for authenticating thereof is examined in more details in reference to Figs. 7 and 8. Fig. 7 is a detailed block diagram illustrating specifically the constitution of a watermark authentication server referring to Fig. 5, and Fig. 8 is a flow chart illustrating a process of comparing a watermark of a card according to the constitution referring to Fig. 7. Each of the blocks constituting watermark authentication server in Fig. 7 is identical to constituent elements of the watermark embedding unit mentioned previously. Thus, the explanation regarding each of the functions will be omitted, but the whole operation is described hereinbelow.

The watermark-embedded digital image processed by the digital image data processing unit 250 is inputted into gray image / color image discriminating device 410 (S400). The gray image / color image discriminating device 410 determines whether the watermark-embedded digital image is a gray image or a color image (S410). If the watermark-embedded digital image is a gray image, a frequency domain transform is carried out regarding luminance components by frequency domain transforming device 430 (S420). If a color image, first, transform to color model such as HSB mode, YIQ mode or YcbCr mode, etc. is executed by the color model transforming device 420 (S430). As to the luminance components, the frequency domain transform such as DCT, DWT, FFT, etc. is carried out.

The watermark embedded ^• in the digital image is detected from the transforming coefficient which is obtained after frequency domain transform regarding watermark-embedded digital image as the above, and the original watermark is restored (S450). The extraction of the watermark is an inverse processing of a process wherein the watermark is multiplied to the result of a characteristic function applied to a predetermined coefficient of a specific frequency domain, and inserted to other predetermined coefficient of a specific frequency domain. From the watermark-embedded digital image, the replacement coefficient (FOF) embedded in the aforementioned specific frequency domain, and the embedding coefficient (FOI) used in calculating the replacement coefficient (FOI') are obtained, and the watermark is restored using these embedding coefficient and the replacement coefficient.

Also, the watermark generating unit 290 receives user keys, and encrypts them by the user key encryption device 440 in the same method as with the watermark embedding process. Then, watermark (W) is generated at the pseudo random number generation device 450 by PN-code method. The generation of watermark includes, other than a method for generating the watermark from user key, for example, a method wherein any one of watermark is embedded and extracted from the various watermarks previously stored in the predetermined storage medium. As to a case wherein the user key is not inputted, the watermark obtained from the embedding coefficient and the replacement coefficient may be compared with various watermarks previously stored to determine whether a predetermined watermark has been embedded.

By analyzing the correlation between the aforementioned restored watermark (WE) and the watermark (W) generated by the method used at the watermark embedment, whether a predetermined watermark is in the digital image can be detected (S460). However, if the watermark has a sequence containing a predetermined-size value, embedding coefficient and replacement coefficient should be used in order to restore the watermark. For instance, if the watermark is a binary sequence having only 1 and -1, under the assumption that the value of a characteristic function fx is always positive numbers, the value of the watermark can be restored only with a plus/minus sign of the replacement coefficient.

The correlation analysis carried out in the comparison operation unit 280 finds the correlation and computes its correlation values between the extracted watermark (WE) and the watermark (W) generated by using the keys inputted by the user, and confirms that the watermark designated by the user has been embedded.

Thus, the authenticity and alteration of the digital image examined by the apparatus for authenticating a card 200 can be known.

Hereinbelow, the method for finding the correlation between two watermarks (WE and W) and for computing their correlation values is explained.

The correlation between two watermarks (WE and W) can be obtained from the following Equation 6.

[Equation 6]

wherein, FF-τ r) represents a conjugate complex number, and IFFT (W) represents inverse FFT (W). The result of the correlation computed from the above Equation 6 is not a certain value, but a sequence form (x_1; ... , x_N). Thus, the computed plurality of values (x_! ~ x_N) is compared, and the maximum peak value M and its position P are obtained. Then, from the result of the correlation acquired from Equation 6, acuity, i.e, 4th moment (Kurtosis) K is computed from the following Equation 7:

[Equation 7]

wherein, x_1? ... , x_N is a sequence obtained from Equation 6 as aforementioned, and is a result value of the correlation between two watermarks (W and WE), x is the mean value of x_1? ... , x_N , and σ represents a standard deviation.

In analyzing the correlation values K, M, and P obtained as above, it is possible to determine whether the watermark (W) generated by a predetermined user key corresponds to the detected watermark (WE). In more detail, if correlation value K, i.e. Kurtosis is less than a predetermined critical value, it means that two watermarks (W and WE) do not correspond to each other, and when the maximum peak value (M) is also less than a predetermined value, it intends that two watermarks (W and WE) do not correspond to each other. Also, only when the position (P) of the maximum peak value of two watermarks (W and WE) is always identical, it is deemed that two watermarks (W and WE) correspond to each other.

Further, the pseudo random number generated from the watermark generating unit has a correlation value of '0' with pseudo random number except for the signal of its own. Thus, when the correlation in accordance with pseudo random number is the predetermined critical value or more, it is deemed that two watermarks (W and WE) correspond to each other. Accordingly, if the digital image satisfies all the requirements of the above correlation values, it is deemed that two watermarks

(W and WE) correspond to each other. Thus, the authentication of the digital image can be confirmed.

Industrial Applicability As aforementioned, according to the present invention authenticating by using a watermark-embedded card, the prevention of illegal acts committed against cards such as credit cards, IC cards, smart cards, student cards, employee cards, card key, etc. can be obtained concurrently with an effect of easily detecting instances wherein such cards have been forged or altered, and an effect of authentication confirming/determining authenticity of a card and a cardholder. Particularly, if linked to database system, the identity information other than the authentication of genuineness of a card can be determined simultaneously. Also, since the card is not affected by contact made to a magnetic body, etc., handling thereof is useful.

Until now, preferable embodiments regarding apparatus and method for producing and authenticating watermarked card are disclosed and explained in examples. However, it is obvious to a person skilled in the pertinent technical field that such embodiments are merely for examples, which are not restricted thereto, and can be in various manner changed or transformed, substituted and replaced within the scope of the technical ideas of the present invention. Also, it must be understood that the technical idea of the present invention is not limited to the aforementioned embodiments, but is limited only in accordance with, the enclosed claims and the technical principle equal thereto.

Claims

What is claimed is:

1. An apparatus for producing a card which contains information for authentication, comprising : means for storing information for issuing a card and information for authenticating a card from a card issuance applicant; means for transforming said information for issuing a card in said means for storing into a digital image having a predetermined size; means for setting said information for authenticating a card in said means for storing to a user key and generating a watermark using said user key; means for embedding said watermark in said digital image; and means for printing a watermark-embedded digital image on the card material.

2. The apparatus according to claim 1, wherein said means for generating comprises : means for encrypting said user key; and means for generating the watermark in pseudo random number form using said encrypted user key.

3. The apparatus according to claim 2, wherein said means for embedding comprises : frequency domain transform means for transforming a luminance component of said digital image into coefficients of a frequency domain; watermark embedding means for embedding the watermark in said digital image by replacing a coefficient of a second frequency band of the coefficients of said frequency domain with a coefficient of a first frequency band of the coefficients of said frequency domain and a replacement coefficient generated using said watermark; and inverse frequency domain transform means for performing an inverse frequency domain transform of said digital image which is transformed to said frequency domain and in which the watermark is embedded.

4. The apparatus according to claim 3, further comprising gray image / color image discriminating means for discriminating whether said digital image is a gray image or a color image, and in case where said digital image is the color image, the apparatus further comprising : color model transform means for transforming said digital image into a color model that includes the luminance component, and extracting the luminance component of said transformed color model to provide it to said frequency domain transform means; and inverse color model transform means for performing a color model inverse transform of said digital image transformed from said inverse frequency domain transform means, by using the luminance components for which said inverse frequency domain transform is performed, and the remaining components with the exception of said luminance components for which said frequency domain transform is not performed.

5. The apparatus according to claim 4, wherein the watermark embedded in said digital image by said embedding means is set for the position thereof in advance.

6. The apparatus according to claim 4, wherein the watermark embedded in said digital image by said embedding means is embedded along with a specific identifier indicating the position to be embedded.

7. A method for producing a card which contains information for authentication, comprising the steps of : transforming information for issuing a card from information for issuing a card and information for authenticating a card from a card issuance applicant into a digital image having a predetermined size; setting said information on authentication of a card to a user key and generating a watermark using said user key; embedding said watermark in said digital image; and printing a watermark-embedded digital image on the card material.

8. The method according to claim 7, wherein said generating comprises the steps of : encrypting said user key; and generating the watermark in pseudo random number form using said user key.

9. The method accordmg to claim 8, wherein said embedding comprises the steps of : transforming said luminance component of said digital image into coefficients of a frequency domain; embedding the watermark in said digital image by replacing a coefficient of a second frequency band of the coefficients of said frequency domain with a coefficient of the first frequency band of the coefficients of said frequency domain and a replacement coefficient generated using said watermark; and performing an inverse frequency domain transform which performs inverse frequency domain transform of the digital image which is transformed to said frequency domain and in which said watermark is embedded.

10. The method according to claim 9, wherein said digital image is color image, said method further comprising the steps of : transforming said digital image into a color model that includes the luminance component, and extracting the luminance component of said transformed color model prior to transforming it into said coefficients of said frequency domain; and performing an inverse color model transform using the luminance component and the remaining components with the exception of said luminance component for which said frequency domain transform is not performed.

11. The method accordmg to claims 9 or 10, wherein said first frequency band is a low frequency band, and said second frequency band is a high frequency band.

12. An apparatus for authenticating a card produced by the method of any one of claims 9 to 11, comprising : means for generating said digital image by scanning said image printed on a card; means for allowing a cardholder to input the information for authenticating a card; and means for determining whether the card to be authenticated by calculating correlation between the watermark generated using the information for authenticating a card inputted by a cardholder and the watermark extracted from said digital image.

13. The apparatus according to claim 12, wherein said means for determining comprises : means for generating the watermark using the information for authenticating a card inputted by a cardholder; means for extracting the watermark for detecting the watermark embedded in said digital image to restore it; and means for determining whether the card is authentic by calculating the correlation between said generated watermark and said restored watermark.