1. A method of determining variations of a test image with respect to a reference image, the method comprising: a) storing the reference image in a memory, wherein the reference image comprises a plurality of pixels, wherein each of the pixels comprises at least one value; b) storing the test image in a memory, wherein the test image comprises a plurality of pixels, wherein each of the pixels comprises at least one value; c) selecting a test image pixel; d) determining an average of the values of one or more pixels in the reference image, wherein the one or more pixels are offset from a pixel in the reference image that corresponds to the location of the test image pixel in the test image; e) determining an absolute difference between a value of the test image pixel and the average value of the offset one or more pixels in the reference image; f) comparing the absolute difference with a maximum difference; g) repeating steps c), d), e), and f) for a plurality of test image pixels; and h) generating a test result, indicative of the variations of the test image with respect to the reference image, using the absolute difference values.