1. A method, by one or more computing devices, comprising: receiving, at a computing device, a message including an image and a current location of a first user, the message sent by a photo-tagging application hosted on a computing device of the first user; accessing a data store to retrieve a set of social contacts associated with the first user; accessing spatio-temporal information for one or more social contacts identified in the set of social contacts; prior to conducting a face matching procedure based on the image, ranking the set of social contacts based on spatio-temporal proximity to the current location of the first user; and sending identifiers corresponding to the one or more top ranked social contacts in the set of social contacts to the photo-tagging application hosted on the computing device of the first user.