13. A non-transitory computer-readable medium storing software comprising instructions executable by one or more computers which, upon such execution, cause the one or more computers to perform operations comprising: receiving a first search query that includes one or more query terms that identify a viewpoint in which an object is to appear in images that are identified in response to the first search query; in response to receiving the first search query that includes one or more query terms that identify the viewpoint in which the object is to appear in images that are identified in response to the first search query, generating a second search query that includes (i) one or more query terms that refer to a category including the object, and (ii) one or more query terms that identify the viewpoint in which the object is to appear in images that are identified in response to the first search query; obtaining (i) a first set of one or more images that are identified as responsive to the first search query, and (ii) a second set of one or more images that are identified as responsive to the second search query; and selecting one or more of the images of the first set based at least on an indication of visual similarity between the selected one or more images and the one or more images of the second set of one or more images.
13. A non-transitory computer-readable medium storing software comprising instructions executable by one or more computers which, upon such execution, cause the one or more computers to perform operations comprising: receiving a first search query that includes one or more query terms that identify a viewpoint in which an object is to appear in images that are identified in response to the first search query; in response to receiving the first search query that includes one or more query terms that identify the viewpoint in which the object is to appear in images that are identified in response to the first search query, generating a second search query that includes (i) one or more query terms that refer to a category including the object, and (ii) one or more query terms that identify the viewpoint in which the object is to appear in images that are identified in response to the first search query; obtaining (i) a first set of one or more images that are identified as responsive to the first search query, and (ii) a second set of one or more images that are identified as responsive to the second search query; and selecting one or more of the images of the first set based at least on an indication of visual similarity between the selected one or more images and the one or more images of the second set of one or more images. 14. The medium of claim 13 , wherein generating a second search query that includes (i) one or more query terms that refer to a category including the object, and (ii) one or query terms that identify the viewpoint in which the object is to appear in images that are identified in response to the first search query, comprises: determining the category associated with the object based at least on the first search query; and determining one or more query terms that are not included in the first search query and that refer to the category.