Patent ID: 6990584

Claim:
A method of restricting a copy of digital information comprising: a detecting process of detecting a first watermark, which is buried in the digital information and comprises a first signal generated on the basis of a first rule; and a burying process of burying a second watermark, which comprises a second signal generated on the basis of a second rule and having a structure different from that of the first signal, into the digital information if the first watermark is detected by the detecting process, wherein said burying process buries the second watermark by superimposing the second watermark onto the digital information in which the first watermark is buried, and wherein said burying process comprises a generating process of generating the second signal by using a generation equation, which is different from that used for generating the first signal, to thereby superimpose the second watermark generated by said generating process onto the digital information in which the first watermark is buried.