This paper addresses the problem of concept learning for semantic image retrieval. Two types of semantic concepts are introduced in our system: the individual concept and the scene concept. The individual concepts are explicitly provided in a vocabulary of semantic words, which are the labels or annotations in an image database. Scene concepts are higher level concepts which are defined as potential patterns of co occurrence of individual concepts. Scene concepts exist since some of the individual concepts co-occur frequently across different images. This is similar to human learning where understanding of simpler ideas is generally useful prior to developing more sophisticated ones. Scene concepts can have more discriminative power compared to individual concepts but methods are needed to find them. A novel method for deriving scene concepts is presented. It is based on a weighted concept co-occurrence network (graph) with detected community structure property. An image similarity comparison and retrieval framework is described with the proposed individual and scene concept signature as the image semantic descriptors. Extensive experiments are conducted on a publicly available dataset to demonstrate the effectiveness of our concept learning and semantic image retrieval framework.