This invention allows the encryption side to set whether an image playback apparatus should play back image data in a scrambled state or a non-scrambled state. When a code-block of input image data is an object to be encrypted, it is encrypted. In playing back the data, it is determined whether playback is to be executed by using the encrypted code-block (the scrambling playback mode is to be set). To inhibit use of the encrypted code-block, a terminating marker is placed at the start of the code-block. To use the encrypted code-block, the terminating marker is placed at the end of the code-block.