Copyright is a form of protection provided by the Congress of the United States to the authors of "original works of authorship," including literary, dramatic, musical, artistic, and certain other intellectual works. This protection is available to both published and unpublished works.
In an academic setting there is a "fair use" exception to the permission requirement, but it is only available if you meet the guidelines. If you do not meet the guidelines, permission must be sought. (See the box on the far right for an expanation of fair use.)
A public domain work is a creative work that is not protected by copyright and which may be freely used by everyone. The reasons that the work is not protected include:
(1) the term of copyright for the work has expired
(2) the author failed to satisfy statutory formalities to perfect the copyright, or
(3) the work is a work of the U.S. Government.
from When U.S. Works Pass Into the Public Domain by Lolly Gassaway, University of North Carolina
Digital Copyright Slider - Use this helpful chart created by Michael Brewer & ALA Office for Information Technology Policy to determine if a work is still copyrighted.
Fair Use is a doctrine of the United States copyright law that allows limited use of copyrighted works without seeking permission typically for the purposes of criticism, comment, news reporting, teaching, scholarship, and research. In determining whether or not use of a copyrighted work is fair the following factors should be considered: