To insert a visible watermark to the extent that an original image can be recognized or so as to be adjust the difficulty of noise elimination in accordance with use.

A data inserting part 15 determines a specific block to be a noise data insertion part and a specific coefficient position among blocks from which division result values are acquired on the basis of the designation of a manual operating device such as an unillustrated keyboard and a mouse or on the basis of a simulatedly generated random number. The data inserting part 15 determines an insertion position of data for release being data required to release noise data. The data inserting part 15 respectively adds noise data and inserts bits of data for release into a noise data insertion position in the determined noise data insertion block and an insertion position of the data for release in the determined insertion block of data for release.