Patent ID: 7613320

Claim:
A digital watermark analysis apparatus for specifying at least one of a plurality of identification information items embedded as a plurality of watermark information items in a plurality of legal copies of digital contents used for collusive attacks, from a plurality of illegal copies of the digital contents obtained by collusive attacks made against the legal copies, the digital watermark analysis apparatus comprising: an extraction unit configured to extract a plurality of embedded codes including ranks from the illegal copies, each of the ranks being uniquely numbered among each of the embedded codes and extract, in units of ranks, one of the embedded codes which is estimated to be most frequently used in the collusive attacks; an acquisition unit configured to acquire a plurality of symbols corresponding to the embedded codes and arrange the symbols in accordance with the ranks of the embedded codes, and acquire a first symbol sequence of symbol sequences each of which includes a plurality of the arranged symbols; and a specifying unit configured to specify at least one of the identification information items embedded in the legal copies, based on the first symbol sequence and second symbol sequences uniquely assigned to the identification information items.