There's no one answer as to what constitutes "fair use" of a particular copyrighted work. The answer varies from situation to situation, and only a court can make a definitive decision.
Four factors are considered in all fair use evaluations:
These four factors are not meant to be exclusive and must be examined jointly.
Under the “fair use” rule of copyright law, a person may make limited use of another author’s work without asking permission.
Important Notice: Use of copyrighted materials for papers, theses, classroom presentations and other academic purposes does not mean that use is automatically fair use. Permission may still be required.
Here are some general Fair Use guidelines for research/teaching.
How much can I use?
Best practice for distributing copies:
Best practice for Internet sources:
Specific Sources for Educators and Librarians:
For additional Fair Use information, check these sites.