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 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The fact that a work is unpublished shall not itself bar a finding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
Or you can read it online here
http://www4.law.cornell.edu/uscode/17/107.html
I am not a lawyer and anyone needing legal advice should seek an
attorney.