A method and system for authenticating a postage indicium on a mail piece. The method comprises the steps of providing a first pattern containing encrypted information in a printed area, engaging a mask with the printed area, wherein the mask comprises a second pattern for forming with the first pattern...http://www.google.fr/patents/US6390377?utm_source=gb-gplus-shareBrevet US6390377 - Hidden information on a mail piece for authentication
Hidden information on a mail piece for authentication
