1. An image processing apparatus having a receiving component configured to receive an image from an image reading device capable of optical scaling, the image processing apparatus comprising: a controller, arranged to: digitally return an optically scaled image received by the receiving component to a full scale image and detect encoded information from the full-scale image in a case where a scaling factor instructed by a user indicates enlargement which does not cause any calculation error when returning an optically scaled image to a full-scale image, and detect encoded information from an image received by the receiving component and digitally scale the image received by the receiving component in a case where a scaling factor instructed by a user indicates enlargement which causes a calculation error when returning an optically scaled image to a full-scale image.