1. A computer-implement method comprising: obtaining a classification response map for an input image using a baseline detector; generating a first-order descriptor, a first-order descriptor comprising a set of binary values in which each binary value is obtained by assigning a binary value based upon comparison of a pair of classification response values selected from the classification response map; and generating a higher-order co-occurrence descriptor by performing the steps comprising: calculating closeness vectors for a set of pairs of classification response values used to form the first-order descriptors relative to a local scan window; generating a histogram of the closeness vectors; and generating the higher-order co-occurrence descriptor as a cross product of the histogram.