1. A method for determining a feature in a subject image, comprising: performing a sparse transform on a subject image, wherein the sparse transform is selected from a group comprising a wavelet transform and a Fourier transform, to determine a sparse transformed subject image that represents the subject image with a few significant coefficients compared to a number of values in the subject image at each of a plurality of orientations; receiving a plurality of number I of patch functions that each is based on a portion of a sparse transformed image at corresponding orientations for a selected image of a training set of images, wherein the plurality of patch functions represent learned features in the training set; and sending data that indicates a feature in the subject image based on the transformed subject image and the plurality of patch functions.