Systems and methods provide for quantifying the similarity between images that appear similar. Given a set of images, one image is selected as the base image, to which the remaining images are compared. One or more portions of the base image are selected for comparison and the color composition of these areas is calculated. Then, the color compositions are examined to quantify the similarity or difference between the images, which is assigned a score reflective of the quantitative similarity or difference. The results are displayed. These systems and methods allow, e.g, a website owner to check whether web pages have come through imperfectly across different browsers; the analysis identifies not just blatant errors, but even single-pixel shifts.