1. A method performed by data processing apparatus, the method comprising: identifying a set of resources, each resource including at least one image and referencing at least one entity; for each image included in at least one of the resources: determining, for each of one or more entities, an overall entity score for the image and the entity based on (i) an entity-image score that specifies a measure of topical relatedness between the image and the entity and (ii) an entity-resource score that specifies a measure of topical relatedness between the entity and a resource that includes the image; and assigning the image to a particular entity from among the one or more entities based on the overall entity score for the image and the particular entity; for each individual entity referenced by at least one of the resources: identifying a group of images that have been assigned to the individual entity; determining an image rank score for each particular image in the group, the image rank score for each particular image being determined based at least on visual characteristics of the particular image; and selecting, as a single image evocative of the individual entity, an image from the group based on the image rank scores.