Patent ID: 7748051

Claim:
A contents server distributing digital contents via a network in response to an acquisition request from outside, said contents server comprising: a contents storage part for storing a plurality of first digital contents wherein a different first digital watermark is embedded; a storage device containing first embedment information; and a first digital contents information adding part comprising: a content selector for: inputting a first digital watermark embedded digital contents Ce 0 and a second digital watermark embedded digital contents Ce 1 , wherein Ce 0 and Ce 1 are unique to one of a plurality of acquisition requestors requesting second digital content, and wherein Ce 0 and Ce 1 are calculated responsive to intensity of the first digital watermark, and selectively switching and outputting the plurality of first digital contents; wherein Ce 0 and Ce 1 are calculated responsive to intensity of said first digital watermark, and a pseudo random number generator for: controlling said content selector to output a predetermined number of partial sets Ce 0 (n) of Ce 0 and a predetermined number of partial sets Ce 1 (n) of Ce 1 and a predetermined number of partial sets C(n) of C; generating an embedded second digital watermark content Cf; wherein the predetermined number of partial sets Ce 0 (n), Ce 1 (n),and C(n) are greater than one; and wherein the partial set Ce 0 (n)=C(n)−ap(n) and the partial set Ce 0 ( 1 )=C(n)+ap(n), where a is a parameter representing the intensity of the embedded second digital watermark, and storing said partial sets Ce 0 (n), Ce 1 (n) and C(n) to a predetermined storage device; and synthesizing said first digital contents for the one of the plurality of acquisition requesters, adding to the first digital contents information specified by the first digital watermark that is different for each of the plurality of acquisition requesters, said first digital contents information responsive to the first embedment information; wherein the first embedment information is responsive to time of distribution of the first digital contents.