Fair use is an exception to copyright codified at Section 107 of the Copyright Act. Under fair use, you may use copyrighted material without permission.
Four factors are considered in determining whether or not a particular use is fair or not. No single factor dictates whether a particular use is fair use. All four factors must be considered in making a determination.
Factor 1: Purpose - Purpose & character of the use.
Fair use favors any use that is nonprofit, educational or personal, especially if it is for teaching, research, scholarship, criticism, commentary, or news reporting. Fair use does not favor uses that are commercial, for profit, or for entertainment purposes. It is important to remember that not all educational uses are fair use. Transformative uses that transform or modify the original purpose of the work and contribute new intellectual value to the original work are often considered fair use.
Factor 2: Nature - The nature of the copyrighted work.
Since authors should have final say over when and how their works are published, fair use tends to favor published works over unpublished works. In addition, factual works are more likely to be considered available for fair use than creative works such as art, music, novels, films, and plays.
Factor 3: Amount - Amount & substantiality of the portion used in relation to the copyrighted work as a whole.
Using a small amount generally favors fair use, whereas using a large amount weighs more against fair use. However, even a small amount of a work can be too much if it can be considered the heart of the work.
Factor 4: Market - Effect of the use upon the potential market for, or value of, the copyrighted work.
Does the use deprive the copyright owner of income or undermine a new or potential market? If so, the use does not favor fair use.
Useful Tools in Determining Fair Use