1. A computer-implemented method comprising: under the control of one or more computer systems configured with executable instructions, defining a contour corresponding to an item represented in an image; determining a number of contour pixels in each of a plurality of radial-polar bins of the image; based at least in part on the number of contour pixels in each of the plurality of radial-polar bins, determining an orientation of the item in the image; and classifying the image based at least in part on the orientation of the item.