10. A method implemented in a data processing apparatus, comprising: determining, by the data processing apparatus and in response to an image insertion request specifying a request to insert image search results referencing images that are responsive to a search query into a list of general search results, an insertion score that defines an ordinal insertion position at which an image display environment in which the image search results are to be displayed is to be inserted into a ranking of the general search results that defines ordinal positions for each of the general search results, the insertion score determined, in part, from quality scores of the images; generating, by the data processing apparatus, a search results resource for displaying the general search results according to respective ordinal positions and the image display environment at an ordinal insertion position within the respective ordinal positions on a client device; and providing the search results resource in response to the search query; wherein each of the image search results is a generated from a search of an image corpus, and each general search result is generated from a search of a resource corpus that is different from the image corpus.
10. A method implemented in a data processing apparatus, comprising: determining, by the data processing apparatus and in response to an image insertion request specifying a request to insert image search results referencing images that are responsive to a search query into a list of general search results, an insertion score that defines an ordinal insertion position at which an image display environment in which the image search results are to be displayed is to be inserted into a ranking of the general search results that defines ordinal positions for each of the general search results, the insertion score determined, in part, from quality scores of the images; generating, by the data processing apparatus, a search results resource for displaying the general search results according to respective ordinal positions and the image display environment at an ordinal insertion position within the respective ordinal positions on a client device; and providing the search results resource in response to the search query; wherein each of the image search results is a generated from a search of an image corpus, and each general search result is generated from a search of a resource corpus that is different from the image corpus. 18. The method of claim 10 , wherein determining an insertion score further comprises: determining a clustering score that measures a clustering characteristic of images that are responsive to the search query; determining an image intent score for the search query; determining a query length score that is proportional to a number of query terms in the search query; and determining the insertion score from the image intent score, the clustering score, and the query length score.