A CPU 200 compares a luminance distribution characteristic of image data with a reference luminance distribution characteristic, and then confirms that the image data GD is a backlit portrait image data if similarity degree Sv between the luminance distribution characteristic of image data and the reference luminance distribution characteristic is larger than reference similarity degree Svref. The CPU 200 determines whether an outer dark portion ratio Do is larger than a reference dark portion ratio Doref. If the CPU 200 determines that the outer dark portion ratio Do is larger than the reference dark portion ratio Doref, then it determines whether an outer bright portion ratio Bo is larger than a reference bright portion ratio Boref. If the CPU 200 determines that the outer bright portion ratio Bo is larger than a reference bright portion ratio Boref, then it determines that the image data GD is image data of backlit portrait image.