15. A system, comprising: a data store storing queries that were previously received from users and data identifying images that were referenced in search results responsive to the queries; and an image quality subsystem coupled to the data store, the image quality subsystem including at least one processor operable to compute, for a query, query specific quality scores for images based on initial quality scores for the images and a transformation factor for the query, the transformation factor for the query representing a measure of importance of image quality for computing relevance scores for the images for the query, the transformation factor being selected based, at least in part, on a comparison of a first number of previous user selections of high quality images for the query to a second number of previous user selections of high quality images for one or more other queries, a high quality image being an image having an initial quality score that meets a threshold score.
15. A system, comprising: a data store storing queries that were previously received from users and data identifying images that were referenced in search results responsive to the queries; and an image quality subsystem coupled to the data store, the image quality subsystem including at least one processor operable to compute, for a query, query specific quality scores for images based on initial quality scores for the images and a transformation factor for the query, the transformation factor for the query representing a measure of importance of image quality for computing relevance scores for the images for the query, the transformation factor being selected based, at least in part, on a comparison of a first number of previous user selections of high quality images for the query to a second number of previous user selections of high quality images for one or more other queries, a high quality image being an image having an initial quality score that meets a threshold score. 18. The system of claim 15 , wherein the image quality subsystem is further operable to select a transformation factor for a query based on quality measures of images that were previously selected for presentation from search results for the query.