System, method of detecting alternation of printed matter, and storage medium

A method of detecting an alteration of a printed matter, printed from an original image, the method comprising:

• embedding a digital watermark data in the original image, wherein the original image is divided into a plurality of blocks each block having been embedded with a pattern corresponding to each value of the digital watermark data;
• storing, in a memory, the original image, the digital watermark data embedded in the original image, and an embedding position of the pattern of the digital watermark data in association with each other;
• detecting a pattern in a scanned image of the printed matter;
• decoding the detected pattern to acquire digital watermark data included in the scanned image;
• aligning each block between the original image and the scanned image, based on the embedding position of the pattern associated with the original image and a detection position of the pattern detected from the scanned image;
• and
• obtaining a difference between the original image and the scanned image aligned with each other to detect an alteration of the printed matter.

A non-transitory computer readable storage medium storing one or more instructions that, when executed by one or more processors, cause the one or more processors to perform a method of detecting an alteration of a printed matter, printed from an original image, the method comprising:

• embedding a digital watermark data in the original image, wherein the original image is divided into a plurality of blocks each block having been embedded with a pattern corresponding to each value of the digital watermark data;
• storing, in a memory, the original image, the digital watermark data embedded in the original image, and an embedding position of the pattern of the digital watermark data in association with each other;
• detecting a pattern in a scanned image of the printed matter;
• decoding the detected pattern to acquire digital watermark data included in the scanned image;
• aligning each block between the original image and the scanned image, based on the embedding position of the pattern associated with the original image and a detection position of the pattern detected from the scanned image;
• and
• obtaining a difference between the original image and the scanned image aligned with each other to detect an alteration of the printed matter.