Patent ID: 7440143

Claim:
An encrypting system for judging whether or not a content of a specified document has been tampered comprising: a document/image output device having a first original image feature information extracting section to divide an original document image of an original document into a plurality of original blocks and to respectively extract original image feature information from the plurality of original blocks, a first encryption key generating section to generate a first encryption key from the extracted original image feature information, a hidden information encrypting section to encrypt specified hidden information using the generated first encryption key, an encrypted information adding section to add the encrypted hidden information to said original document image, and an output section to output said original document image to which said encrypted hidden information has been added; and a decoding device having an image reading section to read an image including a current document image of a current document and the encrypted hidden information, an encrypted information extracting section to divide the current document image into a plurality of current blocks to correspond to the plurality of original blocks and to respectively extract said encrypted hidden information from the current document, a second image feature information extracting section to extract second image feature information representing current features of an image from the current document, a second encryption key generating section to generate a second encryption key from the extracted second image feature information, and a decoding section to perform decoding processing on said extracted hidden information and the current features using the generated second encryption key.