1. A system, comprising: a descriptor processor, configured to receive a local descriptor describing a first object in an image with a respective local label that refers to the first object in the image described by the local descriptor, to receive one or more nearest neighbor descriptors with respective labels, wherein each of the nearest neighbor descriptors meets a threshold measure of similarity to the local descriptor in a database of descriptors and each of the nearest neighbor descriptors describes an object in an image different from the image and has a respective label that refers to the object, and to determine an efficacy of the local descriptor in identifying the first object based on a quality score of the local descriptor and a number of all nearest neighbor descriptors; and a score calculator in communication with the descriptor processor and configured to calculate the quality score for a local descriptor is based on a number of nearest neighbor descriptors with a label equivalent to the label of the local descriptor, and further configured to provide the quality score to the descriptor processor.