The present invention relates to an image processor that is configured to compare a single frame included in the received signal with a preceding processed frame so as to detect changes. In order to enable the image being compressed in as compact a format as possible, the processor is configured to detect changes by dividing the pixels of a single frame into movement blocks and to detect the movement block as changed if in said movement block there is a given number of pixels whose color value change as compared with the corresponding pixels of the preceding processed frame exceeds a predetermined threshold, to exchange the color values of the pixels of the unchanged movement blocks in the frame under process for predetermined values and to generate a signal that indicates the changes.