8. A system comprising: one or more computers and one or more storage devices storing instructions that are operable, when executed by the one or more computers, to cause the one or more computers to perform operations comprising: receiving an initial search query that includes (i) one or more query terms associated with an object, and (ii) one or more query terms that identify a context in which the object is to appear in images that are identified in response to the initial search query; determining a category associated with the object; generating a generalized search query that includes (i) one or more query terms associated with the category, and (ii) one or query terms that identify the context in which the object is to appear in images that are identified in response to the initial search query; obtaining (i) an initial set of one or more images that are identified as responsive to the initial search query, and (ii) a generalized set of one or more images that are identified as responsive to the generalized search query; and selecting one or more of the images of the initial set based at least on an indication of similarity between the selected one or more images and the one or more images of the generalized set of one or more images.
8. A system comprising: one or more computers and one or more storage devices storing instructions that are operable, when executed by the one or more computers, to cause the one or more computers to perform operations comprising: receiving an initial search query that includes (i) one or more query terms associated with an object, and (ii) one or more query terms that identify a context in which the object is to appear in images that are identified in response to the initial search query; determining a category associated with the object; generating a generalized search query that includes (i) one or more query terms associated with the category, and (ii) one or query terms that identify the context in which the object is to appear in images that are identified in response to the initial search query; obtaining (i) an initial set of one or more images that are identified as responsive to the initial search query, and (ii) a generalized set of one or more images that are identified as responsive to the generalized search query; and selecting one or more of the images of the initial set based at least on an indication of similarity between the selected one or more images and the one or more images of the generalized set of one or more images. 12. The system of claim 8 , the operations comprising generating the indication of similarity based on: training an image classifier using the one or more images of the generalized set of one or more images; and determining to generate the indication of similarity based on classifying the selected one or more images using the trained image classifier.