When a CG object is overlapped onto a photographed real scenery image as a background and an image of a photographed real photographic subject is synthesized in front of the overlapped image, an image in which the photographed real background and the photographic subject are imaged simultaneously without imaging the photographed real background and the photographic subject independently, is synthesized with CG. A photographed real image including a specific image is acquired, and area information representing an area of the specific image from the photographed real image, and an area other than the area of the specific image of the photographed real image is synthesized with a computer graphics image using the area information so detected.