The positional offset of an image is corrected without performing any processing for the setting of a reference position with respect to a document image, e.g., the setting of markings. Pieces of information about a reference image, including a reference position, are stored in a predetermined storage unit. Information about the input image is extracted from the input image, and a target position on the input image is calculated on the basis of the extracted information. In addition, a reference image with respect to the input image is specified on the basis of the information about the input image from the predetermined storage unit. The positional offset of the target position with respect to the reference position of the specified reference image is calculated. The positional offset of the input image with respect to the reference image is corrected on the basis of the calculated positional offset amount.