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.

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

• Purpose & character
  • Purpose: Is the copyrighted material being used for commercial or nonprofit educational purposes? Fair use favors educational purposes, but commercial entities can also take advantage of fair use
  • Character: Is the use of the copyrighted material transformative? (i.e. subjected to scholarly analysis, remixed, parodies, etc.)
• Nature of the work
  • Has the work been previously published? Is the work primarily factual or creative in nature? Is this work created and/or marketed as a textbook or an educational consumable (i.e. workbook, etc.)?
• Amount
  • How much of the work is being used? How important is the portion being used? If you are using the whole work, is it clear that no less than the whole work will be effective (i.e. photograph, poem, etc.)?
• Effect 
  • Is the work in-print? Is it available licensed elsewhere? Is there a market for the work? Can you identify the copyright holder? Did the copyright holder respond to a request for permission? Did you acquire this copy legally? Will you be able to attribute the original author?

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, therefore, it is advisable to treat the four factors equally.