To make a reasonable judgment about whether the use you make of a copyrighted work is Fair Use, the Copyright law provides a set of four criteria in Sec.107. These criteria include:
It is important to note that while no one factor is paramount, all four factors should be considered in your analysis. Note also that the preamble to Sec. 107 lists criticism, commentary, news reporting, teaching (including multiple copies for classroom use), scholarship, or research as examples of Fair Use. That does not mean that ALL use for these purposes are necessarily Fair Use, but it does point to the purposes that Congress had in mind when writing Sec. 107.