Image AFter: A large online free photo collection (Students can download and use any image or texture from the site for their own work, either personal, educational, or commercial.)
NASA Photo Library: NASA still images, audio files, and video generally are not copyrighted. You may use NASA imagery, video, and audio material for educational or informational purposes, including photo collections, textbooks, public exhibits, and Internet Web pages. This general permission extends to personal Web pages. http://nix.larc.nasa.gov/