An image processing system includes: an image input unit which reads an image printed on a medium and generates electronic data representing the image; and a processing unit which corrects the image represented by the electronic data. The processing unit implements the functions of: detecting, from the image represented by the electronic data, a first pattern having a first size and shape that is attached to the image; measuring a degree of degradation by measuring an amount of displacement of the size of the detected first pattern from the first size; and correcting the image represented by the electronic data to reduce the degree of degradation.