1. A method comprising a plurality of acts that are executed by a processor, the acts comprising: encoding a first descriptor for a first image patch, wherein the first image patch is a portion of a first digital image, and wherein encoding the first descriptor for the first image patch comprises normalizing a magnitude of a gradient corresponding to an edge in the first image patch, wherein normalizing the gradient comprises normalizing the gradient based at least in part upon an average gradient magnitude in a spatial neighborhood that is within a threshold number of pixels from a pixel corresponding to the gradient; comparing the first descriptor for the first image patch with a second descriptor for a second image patch, wherein the second image patch is a portion of a second image; and outputting an indication that the first digital image and the second digital image comprise a substantially similar object based at least in part upon the comparing of the first descriptor for the first image patch with the second descriptor for the second image patch.