In order to specify a region on an original on an original plate more accurately, an image processing apparatus, which reads an original placed on an original plate as digital image data using an image reading unit, includes a detection unit which detects a code image, that is recorded on an original and includes reading setting information, from an image read by a prescan using the image reading unit, an extraction unit which extracts the reading setting information from the detected code image, and a reading control unit which executes a main scan using the image reading unit based on the extracted reading setting information, and the reading setting information includes reading range information designated by a relative position to the original that records the code image with reference to the position and direction of the code image.