Copyright is "a property right in an original work of authorship (such as a literary, musical, artistic, photographic, or film work) fixed in any tangible medium of expression, giving the holder the exclusive right to reproduce, adapt, distribute, perform, and display the work."
Garner, B. (Ed.). (2001). Black's Law Dictionary (2nd Pocket ed.). St. Paul, MN: West Group.
Under the "fair use" rule of copyright law, certain uses of copyright protected work may be used without asking permission. Fair use is intended to support teaching, research, and scholarship, but with educational purpose alone does not make every use of a work fair. It is always important to analyze how you are going to use a particular work against the following four factors of 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.