Fair Use is an exception to copyright law and it should only be relied upon after all efforts to secure permission have been exhausted and under very specific circumstances, in consultation with a librarian. "In its most general sense, a fair use is any copying of copyrighted material done for a limited and “transformative” purpose, such as to comment upon, criticize, or parody a copyrighted work. Such uses can be done without permission from the copyright owner. In other words, fair use is a defense against a claim of copyright infringement. If your use qualifies as a fair use, then it would not be considered an infringement." - https://fairuse.stanford.edu/overview/fair-use/what-is-fair-use/
These are the four factors that judges use to weigh fair use cases:
- the purpose and character of your use- If you're using it for educational purposes, that will weigh in your favor
- the nature of the copyrighted work - the more creative the work, the weaker the fair use case
- the amount and substantiality of the portion taken- if you only take a tiny portion- just what you need- rather than using the full copyrighted work, that will weigh in your favor. Only use what you need! There is no specific portion that is always okay to use. Some people say 1/10th of the work or 1 chapter of a book. The law itself does not list any specific amount. If you are going to use an image under Fair Use, consider using a lower resolution image that could not be well reproduced by others, for example.
- the effect of the use upon the potential market- if your use impacts the market such that the copyright owner can make less profit from the work, then that will weigh heavily against you. If your use does not rob the copyright owner of any potential profit, that will weigh in your favor.