Copyright law allows certain 'fair use' provisions for using copyrighted material.
See, 17 U.S.C. § 107 (2011):
§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 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The fact that a work is unpublished shall not itself bar a finding of fair use if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.
Professor Eric Faden of Bucknell University provides this humorous, yet informative, review of copyright principles delivered through the words of the very folks we can thank for nearly endless copyright terms.