A good source if you are looking for image clearance on an art work. The Bridgeman Copyright Service was set up to handle permissions clearances on the entire body of works of an artist or collection regardless of whether The Bridgeman Art Library can provide reproduction materials. See: http://www.bridgemanart.com/copyright
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."