Provided are a specific image information adding method with enhanced detection accuracy enabling multiple pieces of information to be added, and an image forming apparatus using the method. In the method of adding specific image information about a recorded image onto the recorded image, the specific image information consists of reference information and identification information, the reference information is formed so as to be able to set a reference position for reading of the specific image information, and the identification information is formed from dot images indicative of bit information at predetermined positions on an arc or a circumference around the reference position. The identification information can represent a single information item by a plurality of dot images, which are placed on a plurality of different arcs or circumferences and arranged at predetermined spacings in the circumferential direction and in the radial direction.