This invention is an image processing apparatus capable of adding a reference frame for accurately specifying an image region printed on a printing medium. An image forming unit (13) converts an input image for printing into that of a predetermined resolution. An additional information multiplexer (14) embeds additional information in each predetermined region of the resolution-converted image. A reference frame addition unit 15 adds a predetermined reference frame to the perimeter of the image in which the additional information is embedded. A printer (16) prints the image having the additional information embedded in it and the reference frame onto a printing medium, and outputs a printed image (17).