Everystockphoto.com is a license-specific photo search engine. Currently they index and search millions of freely licensed photos, from many sources, and present them in an integrated search. Membership is free and allows you to rate, tag, collect and comment on photos.
Google Image Search is a search service created by Google which allows users to search the Web for image content. The keywords for the image search are based on the filename of the image, the link pointing to the image and text adjacent to the image. When searching for an image, a thumbnail of each matching image is displayed. Then when clicking on a thumbnail, the image is displayed in a frame at the top of the page and the website on which that image was found is displayed in a frame below it, making it easier to see from where the image is coming. WARNING - some of the images you may find using this method may be copyrighted, be careful.
The site provides a library of high-resolution, royalty-free photographs which may be downloaded free of charge for use in design projects. Although images are free, contributors still retain moral rights and photographs are still subject to usage restrictions.