The FAIR USE section of the U.S. Copyright Act
Section 107. Limitations on exclusive rights:
Fair Use.
Notwithstanding the provisions of sections 106 and 106A, the fair use of a
copyrighted work, including such use by reproduction in copies or
phonorecords or by any other means specified by that section, for the purposes
such as criticism, comment, news reporting, teaching (including multiple
copies for classroom use), scholarship, or research, is not an infringement of
copyright. In determining whether the use made of a work in any particular
case is a fair use the factors to be considered shall include-
(1) the purpose and character of the use, including whether such use is of a
commercial nature or is for nonprofit educational purposes;
(2) the nature of the copyrighted work;
(3) the amount and substantiality of the portion used in relation to the
copyrighted work as a whole; and
(4) the effect of the use upon the potential market for or value of the
copyrighted work.
The fact that a work is unpublished shall not itself bar a finding of fair use
if such finding is made upon consideration of all the above factors."
-United States Copyright Act
(17 U.S.C. 107, 1988 ed. and Supp. IV)