FlickrCC

FlickrCC , a search engine drawing solely from Flickr’s Creative Commons licensed images. Really easy to use - search on a theme - results are presented as a wall of thumbnail images, download a range of sizes for use.
Creative Commons Licence definition:
a non-profit organization dedicated to reforming copyright laws to permit the free use, alteration and distribution by others of copyrighted creative works, such as music, film or software.