Cornell University Law School - U.S. Code: Title 17 - COPYRIGHTS
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Stanford University Libraries - What is Fair Use?
United States Copyright Office - U.S. Copyright Office Fair Use Index
Public domain: The realm embracing property rights that belong to the community at large, are unprotected by copyright or patent, and are subject to appropriation by anyone.
http://www.merriam-webster.com/dictionary/public%20domain
Creative Commons: Creative Commons is a nonprofit organization that enables the sharing and use of creativity and knowledge through free legal tools.