19. The non-transitory machine-readable storage medium recited in claim 18 wherein the first data is an image representation comprising a plurality of pixels.
19. The non-transitory machine-readable storage medium recited in claim 18 wherein the first data is an image representation comprising a plurality of pixels. 20. The non-transitory machine-readable storage medium recited in claim 19 wherein the instructions further comprise instructions that cause the at least one machine to: down-sample the pixels of the image to a block of down-sampled pixels; and determine a plurality of spatial frequency values of the block of down-sampled pixels in at least one of the first color space or the second color space, wherein the query feature vector further includes at least one of the spatial frequency values of the input representation image and each of the candidate feature vectors includes at least one spatial frequency value of the respective candidate image.