11. A system, comprising: one or more computers operable to perform operations comprising: obtaining a group of similar images for a particular image, wherein each similar image is associated with one or more n-grams; determining an overall score for each of the n-grams, wherein for each n-gram the overall score is based at least in part on: i) a combination of image specific scores for the n-gram for images in the group of similar images and ii) the number of similar images in the group of similar images; and selecting one of the n-grams as a textual description of the particular image according at least in part on the overall scores for the n-grams and the respective n-gram order of each of the n-grams representing a number of tokens in the n-gram.
11. A system, comprising: one or more computers operable to perform operations comprising: obtaining a group of similar images for a particular image, wherein each similar image is associated with one or more n-grams; determining an overall score for each of the n-grams, wherein for each n-gram the overall score is based at least in part on: i) a combination of image specific scores for the n-gram for images in the group of similar images and ii) the number of similar images in the group of similar images; and selecting one of the n-grams as a textual description of the particular image according at least in part on the overall scores for the n-grams and the respective n-gram order of each of the n-grams representing a number of tokens in the n-gram. 12. The system of claim 11 , wherein obtaining a group of similar images for a particular image comprises querying an index that associates images with descriptors.