1. A server comprising: a communication interface operable to communicatively coupling the server to a network; and a control system comprising at least a processor and a memory storing program codes operable to: obtain social relationship information identifying a social relationship between a reference person and one of a plurality of other subjects that appear in a plurality of images; determine a subject affinity defining a subject affinity score between the reference person and the one of the plurality of other subjects based on the identified social relationship between the reference person and the one of the plurality of other subjects, the plurality of other subjects corresponding to subjects other than the reference person; and determine an image affinity for each of the plurality of images based on the subject affinity for the one of the plurality of other subjects, each image affinity defining an image affinity score between the reference person and a corresponding one of the plurality of images based on the one of the plurality of other subjects appearing in the image.