Fair use (section 107 of U.S. copyright law) provides parameters for the legal use of copyrighted material without the permission of the copyright holder. While only a court can determine if a use is "fair" (and only if a case is litigated), four factors are considered in determining whether one may use copyrighted materials without consent from the copyright holder: purpose, nature, amount, and effect.
Learn more about fair use on copyright.gov.
This tool helps determine the "fairness" of a use under U.S. copyright law by applying the four factors: purpose, nature, amount, and effect.
This site puts its emphasis on copyright issues that affect the education and library community, including examples of fair use and policies.