Google has an image search engine, which claims to be the most comprehensive on the Web, indexing over 150 million images. Keyword searches produce return pages with 20 thumbnails, each of which includes image size information and the URL of the source page. Clicking on a thumbnail produces a framed page with a larger image of the thumbnail above the full page on which the image was found. Users can turn off the frame using a button on the top right. All of the advanced search commands are available with image search, and users can also limit their search to a specific file format. There is an adult content filter option (default is on), but Google warns users that some adult content may potentially slip through.