1. A method for determining facial similarity among images in a social networking service, the method comprising: determining, using at least one processor, inequalities between a plurality of training faces associated with one or more images based on received indications of similarity between a plurality of image groupings; determining, using the at least one processor, a mapping function between an objective feature space and a psychological feature space that indicates human perception of facial similarity based on the inequalities; receiving a query associated with an image that includes a query face; determining, using the at least one processor, one or more search result images from among a plurality of images associated with users of a social networking service based on the mapping function; and providing the search result images to a user of the social networking service.