A method, apparatus, and program for image processing are provided to perform operations for generating an encoded image, detecting image alteration on the encoded image, and regenerating an original image from the encoded image. The encoded image is generated by an encoding apparatus, which inserts a redundant code into an LSB (least significant bit) bit-plane of the original image. The redundant code can be generated based on bit-planes other than the LSB bit-plane, using a CRC (cyclic redundancy check) method. A decoding apparatus recalculates a redundant code from the encoded image, and checks validity of the encoded image based on the extracted redundant code.