The purpose or character of the use: is your use non-profit, educational, personal, commercial?
The nature of the work being used: is your use published, unpublished, factual or creative?
The amount of the work being used: what percentage of the work are you using, is it central and essential?
The impact of use on the market: will your use diminish the market for the original?
Each of these factors plays a role in determining whether or not you may claim fair use. For more information on applying the four factors of fair use visit: Copyright Overview