1. An image processing system comprising: a processor having a memory storing computer-executable instructions, wherein the processor is programmed to: define a first descriptor in a first image; generate a mask from the first image; define a second descriptor in a second image, wherein the first descriptor includes a plurality of first test points and wherein the second descriptor includes a plurality of second test points; compare the first descriptor to the second descriptor to define a first error vector; determine a second error vector by applying the mask, wherein the mask reduces the plurality of first test points to a subset of the plurality of first test points based at least in part on a robustness to viewpoint change of each of the plurality of first test points; and determine an error between the first descriptor and the second descriptor using the second error vector.