Caption Crawler is assistive technology that allows screen reader users to automatically replace bad or missing descriptions of images on their favorite websites with image captions from other pages that have similar images.
Caption Crawler provides a web browser extension and web service. The extension finds images on web pages that do not have any "alt text", i.e., captions provided for the image by the web page author. When it finds such an image, it sends the image's source (i.e., URL) to a web service. That web service uses the Bing Image Search API to request both a caption and known web pages containing the same image (or related image). Any captions found are sent back to the extension to be added as the "alt text" for the image so that a screen reader can read it. Captions are either those returned by the Bing service or else were found by the service from parsing the pages returned by the Bing service.