1. Purpose and character of the use
   Is the use for nonprofit educational or for commercial purposes?
   A particular use is more likely to be considered fair use if it is for nonprofit educational use.


2. Nature of the copyrighted work
   Is the material factual or imaginative?
   A particular use is more likely to be considered fair use if the material is primarily factual.


3. Amount and substantiality of the portion used
   Is a small amount being used to illustrate a point, or is the entire work being used?
   A particular use is more likely to be considered fair use if it is a small portion of the overall piece.


4. Effect of the use upon the potential market or value of the copyrighted work.
   In other words, does using the material compete with potential profits that the owner could be entitled to?
   An instance is more likely to be considered fair use if it is has no impact on potential profits of the copyright owner. (This is often the most difficult factor to overcome.)

There is no strict guidelines for what exactly falls under fair use. You have to use your best judgement. It is hard to define what is a little and what is a lot. As a rule of thumb, you should always try to get permission when using someone else's work. THere have been many court-cases on the issue of fair-use, and as a student you probably want to avoid those expensive lawyer fees.