Flickr - a large database of images
You may know Flickr as a public photo-sharing site with billions of images. In recent years, many archival image repositories (including the Cornell University Library) have begun sharing their copyright-free images via Flickr Commons, which has become a major image resource.
Creative Commons License
Creative Commons "provides free tools that let authors, scientists, artists, and educators easily mark their creative work with the freedoms they want it to carry." You can use CC to change your copyright terms from "All Rights Reserved" to "Some Rights Reserved."