There's no one right answer as to what constitutes a "fair use" of a particular copyrighted work. The answer varies from situation to situation.

A good point to consider is this: Have you made a "good faith" effort to comply with the "fair use" clause of U.S. Copyright Law?

"Four factors" are considered in all fair use evaluations. They are:

1.      Purpose & character

2.      Nature of the work

3.      Amount

4.      Effect 

These four factors are not meant to be exclusive and must be examined together. 

The statute does not indicate how much weight is to be accorded each factor. Historically the courts have placed the most emphasis on "effect", while the "nature" of the copyrighted work is usually considered to be the least important factor.

 An excellent resource to use is the ALA's Fair Use Evaluator.

The Copyright Act gives the owner of a copyright the exclusive right to reproduce and distribute their work. One exception to this exclusive right is called "the fair use exception." The fair use exception permits the reproduction of a small portion of a copyrighted work without the copyright owner's permission, but only under very limited circumstances. The purpose is to allow students, scholars, and critics the right to reference a copyrighted work in their own scholarship, teaching, and critiques.  However, the courts are not bound by these guidelines and the Copyright Act contains no such guidelines, therefore it's advisable that you still conduct a Fair Use Evaluation.

The difference between “fair use” and “infringement” of a copyright-protected work is not easy to determine. The burden of establishing a “fair use” is on the user and requires a very circumstance-specific analysis of the intended use or reuse of a work. Here are three examples that illustrate this challenge:

"Professor Eric Faden of Bucknell University provides this humorous, yet informative, review of copyright principle."