To provide a technology, capable of suitably encrypting and decrypting a partial region to image data to which partial region encryption and multiple encryption are applied, and of acquiring a key required for partial decryption.

A reproduction region designation part 32 acquires a partial image region in the image data; an overlapping discrimination part 33 calculates an overlapping region between the acquired image region and an encrypted region; a decryption key acquisition part 35 acquires key information corresponding to the calculated overlapping region, an encryption sequence specification part 36 specifies encryption processing sequence; and an image decryption part 37 encrypting and decrypting the image data, corresponding to the overlapping region, in response to the specified encryption sequence by using the acquired key information.

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