1. A system, comprising: a descriptor processor, configured to receive a local descriptor relating to an object in an image, to receive nearest neighbor descriptors relating to one or more images different from said image, wherein said nearest neighbor descriptors comprise nearest neighbors of the local descriptor, and to determine the efficacy of the local descriptor in identifying said object based on a quality score of the local descriptor; and a score calculator in communication with said descriptor processor and configured to calculate said quality score based on the number of nearest neighbor descriptors that relate to images showing said object, and further configured to provide said quality score to said descriptor processor, wherein said quality score is calculated according to an equation q ⁡ ( x i ) = K m wherein q is the quality score, x i is the local descriptor, m is the number of said nearest neighbor descriptors, and K is the number of nearest neighbor descriptors that relate to images showing said object.