1. A method comprising, by one or more computer systems: receiving, from a user, a multimedia object, the multimedia object comprising one or more images; applying one or more object image recognition algorithms to the multimedia object; comparing at least a portion of the multimedia object to a plurality of stored images in a database, each of the plurality of stored images associated with a physical location; determining a location of the user based on the comparison; and automatically associating the user with a concept node of a social graph representing a social network, the concept node being associated with the determined location.