Patent ID: 7970139

Claim:
An image reproduction method by which encrypted image data is reproduced, the encrypted image data having a partially encrypted first encryption area and a partially encrypted second encryption area, and at least the first encryption area and the second encryption area partially overlapping each other, comprising: an area acquisition step of acquiring a partial desired reproduction area in the image data; an overlap calculation step of calculating, using a central processing unit, a first overlap area, which is a product set of the first encryption area and the desired reproduction area, and a second overlap area, which is a product set of the second encryption area and the desired reproduction area; a judgment step of judging whether the first overlap area calculated in said overlap calculation step is an empty set, because there is no overlap between the desired reproduction area and the first encryption area, and whether the second overlap area calculated in said overlap calculation step is an empty set, because there is no overlap between the desired reproduction area and the second encryption area; a key information acquisition step of acquiring key information corresponding to an overlap area judged not to be an empty set, in a case where it is judged in said judgment step that at least one of the first overlap area and the second overlap area is not an empty set; a decryption order specifying step of specifying a decryption processing order in the overlap area judged not to be an empty set, using information for specifying an encryption order of the first encryption area and the second encryption area; and a decryption step of executing a decryption process, using the central processing unit, on the image data corresponding to the overlap area judged not to be an empty set, using the key information acquired in said key information acquisition step, in accordance with the decryption processing order specified in said decryption order specifying step.