11. A system, comprising: a data processing apparatus; and a memory coupled to the data processing apparatus having instructions stored thereon which, when executed by the data processing apparatus cause the data processing apparatus to perform operations comprising: receiving data specifying a first image; receiving text labels for the first image; for each of one or more of the text labels: receiving search results in response to a web search performed using the text label as a query, each search result referencing a web resource; assigning a text label ranking score to the text label based on a number of the resources referenced by the received search results that include an image matching the first image; ranking the text labels, at least in part, based on the text label ranking scores assigned to text labels; and selecting an image label for the first image from the ranked text labels, the image label being selected based on the ranking.
11. A system, comprising: a data processing apparatus; and a memory coupled to the data processing apparatus having instructions stored thereon which, when executed by the data processing apparatus cause the data processing apparatus to perform operations comprising: receiving data specifying a first image; receiving text labels for the first image; for each of one or more of the text labels: receiving search results in response to a web search performed using the text label as a query, each search result referencing a web resource; assigning a text label ranking score to the text label based on a number of the resources referenced by the received search results that include an image matching the first image; ranking the text labels, at least in part, based on the text label ranking scores assigned to text labels; and selecting an image label for the first image from the ranked text labels, the image label being selected based on the ranking. 19. The system of claim 11 wherein the text label ranking score for each text label is based on a median search result score calculated according to search result scores associated with the search results, a number of search results returned by the web search, and an original rank position of the received text labels.