Submit an image to TinEye to find out where it came from, how it is being used, if modified versions of the image exist, or to find higher resolution versions.
Image search engine that locates high-resolution images with Creative Commons licenses for use in presentations, blogs, etc. Also retrieves stock photos.
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."