At every reproduction of a moving image, a tamper resistant module (TRM) randomly selects any one of plural electronic watermark inserting modules, and incorporates the module selected into an area randomly selected from among plural non-operation (NOP) areas in an MPEG expansion module. The module can be switched for each image in a series of the moving images. Since an algorithm for inserting the electronic watermark differs for each moving image or each image, elimination of the electronic watermark by means of analysis, particularly, complete elimination from all the images, is extremely difficult.