Tampering judgement system, encrypting system for judgement of tampering and tampering judgement method

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 image feature information extracting section to extract first image feature information representing features of an image from a document image showing a specified document, a first encryption key generating section to generate first encryption key from said first image feature information, a hidden information encrypting section to encrypt specified hidden information using said first encryption key, an encrypted information adding section to add the encrypted hidden information to said document image, and an output section to output said document image to which said encrypted information has been added;
• and
• a decoding device having an encrypted information extracting section to extract said encrypted information from an output document image serving as said document image output by said output section, a second image feature information extracting section to extract second image feature information representing features of an image from said output document image, a second encryption key generating section to generate a second encryption key from said second image feature information, and a decoding section to perform decoding processing on said extracted and encrypted information using said second encryption key.

The encrypting system according to claim5, wherein said encrypted information serves as information representing said encrypted hidden information in a manner that said encrypted hidden information is able to be optically read.

A method for judging whether or not a document image has been tampered which has a document image outputting device and a tampering judgement device, said method comprising:

• a first step of having said document image output device extract first image feature information representing features of an image from a document image representing a specified document, add original image feature information representing said extracted first image feature information to said document image and output said document image to which said original image feature information has been added;
• and
• a second step of, after having completed said first step, having said tampering judgement device extract said original image feature information from an output document image serving as said output image, then extract second image feature information representing features of an image from said output document image and compare said first image feature information represented by said extracted original image feature information with said second image feature information and judge, based on a result from the comparison, whether or not said output document image has been tampered.