Section 107 of U.S. Copyright Law allows for some uses of portions of copyrighted works for purposes such as criticism, comment, news reporting, teaching, scholarship, and research.
Determining Fair Use is done on a case-by-case basis according to the Four Factors of Fair Use:
Each of these factors must be considered and balanced with the others to gain an overall picture of your intended use and to help you reach an informed decision.
These are interactive Fair Use evaluators that may help inform your decision to use copyrighted works.
Remember:
“The distinction between what is fair use and what is infringement in a particular case will not always be clear or easily defined. There is no specific number of words, lines, or notes that may safely be taken without permission. Acknowledging the source of the copyrighted material does not substitute for obtaining permission.” – U.S. Copyright Office