1. A method for retrieving digital images, comprising: while images are viewed in a plurality of Transmission Control Protocol/Internet Protocol (TCP/IP) sessions, storing data that indicates which images are viewed in same sessions; wherein the data indicates that a first set of images were viewed in one or more sessions in which a particular image was also viewed; wherein the data indicates that a second set of images were not viewed in any session in which the particular image was also viewed; receiving, from a client, request data that specifies search criteria; wherein the search criteria identifies the particular image as a base image; in response to receiving the request data, performing the steps of: reading the data to determine that the first set of images, but not the second set of images, were viewed in one or more sessions in which said base image was also viewed, selecting one or more requested images based, at least in part, on whether the images were viewed in sessions in which said base image was also viewed, wherein images in the first set are more likely to be selected than images in the second set because the images in the first set were viewed in one or more sessions in which said base image was also viewed; and transmitting, to the client, response data that identifies the one or more requested images; wherein the step of selecting one or more requested images is performed by one or more computing devices.