Fair Use (Title 17, Section 107 of the Copyright Act) is an exception to copyright law which allows the public limited use of copyrighted material without requiring prior permission from the copyright holder. Fair Use contains a list of the various purposes for which the use of a particular work may be considered fair, such as criticism, comment, news reporting, teaching, scholarship, and research.
Fair Use includes four factors you need to consider when determining if your intended use is a 'fair' one. To apply the factors, you should take your situation and consider each factor:
1. The purpose and character of the use, including whether such use is of commercial nature or is for nonprofit educational purposes. Educational use weighs in favor of fair use and commercial use weighs against fair use.
2. The nature of the copyrighted work. Factual works are given less protection than creative works.
3. The amount and substantiality of the portion used in relation to the copyrighted work as a whole. Generally, a large amount weighs against fair use, whereas a small amount would be considered fair use. There is no magic number or percentage.
4. The effect of the use upon the potential market for, or value of, the copyrighted work. If the intended use would negatively impact sales of the work, then the use would generally weigh against fair use.
All four factors must be taken into consideration but ALL factors do not have to be in favor to make a use a fair one.
If you're still uncertain if your particular use of copyrighted material would fall within 'Fair Use', you can try the following Fair Use evaluator tools to help you determine if your use of copyrighted material is fair or not.