1. An image processing apparatus comprising: code image detection unit that determines whether or not an code image is included in the original image data; code image decoding unit that decodes said code image to extract source data if it is determined that the code image is included by said code image detection unit; and synthesizing unit that encodes information obtained by decoding a partial area of said code image and overlaying encoded information on the area where said code image is included, if said code image decoding unit is successful in decoding only the partial area of said code image.