1. A method implemented on a computing device having a processor for summarizing image search results, comprising: using the computing device having the processor to perform the following: defining an image relevance for each image in the image search results, where the image relevance is a rank of an image in the image search results as ranked by a search engine providing the image search results; computing an image quality for each image based on one or more image quality measures; clustering images in the image search results using a clustering technique that has as a first informative prior the image quality for each image and as a second informative prior the image relevance for each image to obtain a summary candidate collection containing image clusters and an exemplar image for each cluster; selecting and ranking each image in the summary candidate collection to obtain an image search results summarization; and presenting the image search results summarization to a user.