In an image data processing device, a selection unit receives a block of original image data of a current image, a block of compressed and reconstructed image data of the current image, and a block of compressed and reconstructed data of a previous image that precedes the current image. A comparison unit compares the block of compressed and reconstructed image data of the current image with the block of compressed and reconstructed data of the previous image. An output unit, in the event that the comparison of the comparison unit results in a match, outputs the block of original image data of the current image as first output data, and, in the event that the comparison of the comparison unit does not result in a match, outputs the block of compressed and reconstructed data of the previous image as the first output data.