13. The one or more computer-readable hardware storage device of claim 12 the operations further comprising using individual windows of the plurality of windows of computation to divide the pixels of at least one of the listing images into a plurality of areas, and computing a difference in intensity of blackness versus whiteness of at least some of the plurality of areas.
13. The one or more computer-readable hardware storage device of claim 12 the operations further comprising using individual windows of the plurality of windows of computation to divide the pixels of at least one of the listing images into a plurality of areas, and computing a difference in intensity of blackness versus whiteness of at least some of the plurality of areas. 14. The one or more computer-readable hardware storage device of claim 13 wherein each window of computation is a circle and the diameter of each window divides an area of the listing image within the circle into a plurality of regions, the operations further comprising computing the histograms of the pixels that lie in each of the plurality of regions.