1. An image processing system comprising: a processing device having a memory device for storing computer-executable instructions, wherein the processing device 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; compare the first descriptor to the second descriptor to define a first error vector; determine a second error vector by applying the mask; and determine an error between the first descriptor and the second descriptor using the second error vector.