Biomed Search ( http://biomed-search.com ) provides access to images, figures, and schema in biomedical articles. The site currently includes more than 1 million images.
Biomed Images (http://www.biomedimages.com/) provides a similar service for images from open source journals such as Biomed Central.
Both resources index the image captions. Biomed Search also indexes the citations. Both provide links back to the original free/open source article that the image was found in.