3. The method of claim 1 , further comprising: representing, in the data processing system, the reference image and co-selected images as nodes in a weighted graph, each node being connected to other nodes by weighted edges representing sequential selections of the images represented by the node and the other nodes; and wherein the topic score for each co-selected image is generated based on the weighted edges.
3. The method of claim 1 , further comprising: representing, in the data processing system, the reference image and co-selected images as nodes in a weighted graph, each node being connected to other nodes by weighted edges representing sequential selections of the images represented by the node and the other nodes; and wherein the topic score for each co-selected image is generated based on the weighted edges. 7. The method of claim 3 , wherein generating a topic score comprises: for each co-selected image, identifying a weighted edge that connects a node representing the reference image to a node representing the co-selected image; and generating the topic score based on a weight of the weighted edge.