"Fair use," originally a judge-made doctrine, is a statutory defense to copyright infringement. The test for "fair use," articulated in Section 107 of the Copyright Act (17 U.S.C. Section 107), includes four key factors: the purpose and character of the use, including whether such use is of a commercial nature or is for nonprofit educational purposes; the nature of the copyrighted work; the amount and substantiality of the portion used in relation to the copyrighted work as a whole; and the effect of the use upon the potential market for or value of the copyrighted work.