1. An image processing system for comparing images, the system comprising: an object thinning module operable to thin objects in a first monochromic image and thin objects in a second monochromic image, so as to generate a skeleton image of the first monochromic image and a skeleton image of the second monochromic image; an object thickening module operable to thicken the objects in the first monochromic image and thicken the objects in the second monochromic image, so as to generate a bold image of the first monochromic image and a bold image of the second monochromic image; an image overlaying module operable to overlay the skeleton image of the first monochromic image with the bold image of the second monochromic image, and overlay the skeleton image of the second monochromic image with the bold image of the first monochromic image, so as to respectively generate an overlaid image; an image output module operable to output the overlaid images on a display screen; and a processor that executes the object thinning module, the object thickening module, the image overlaying module, and the image output module.