Because there is a sizable gray area in which fair use may or may not apply, there is never a guarantee that your use will qualify as a fair use. The fair use doctrine has been described as a murky concept in which it is often difficult to separate the lawful from the unlawful. 

Two types of situations are especially likely to cause legal problems:  

(1) Your work causes the owner of the original work to lose money. For example, you borrow portions of a biology text for use in a competing biology text. 

(2) The copyright owner is offended by your use. For example, you satirize the original work and your satire contains sexually explicit references or other offensive material. 

Remember, these criteria do not determine whether you will prevail in a fair use lawsuit—they simply indicate whether you are likely to trigger a lawsuit. When you use someone’s work and deprive them of money or offend them, the chances of being sued increase. Just as there are situations that are more likely to cause lawsuits, there are some situations that may lower the risk: You use a very small excerpt of a factual work, for example, one or two lines from a news report, for purposes of commentary, criticism, scholarship, research, or news reporting. You diligently tried to locate the copyright owner but were unsuccessful, and after analyzing the fair use factors, you became convinced that your use would qualify as a fair use.

. Stanford Copyright and Fair Use Center. 

https://fairuse.stanford.edu/overview/fair-use/four-factors/#example

Disagreements Over Fair Use: When Are You Likely to Get Sued?

 Stanford Copyright and Fair Use Center. 

https://fairuse.stanford.edu/overview/fair-use/disagreements-over-fair-use-when-are-you-likely-to-get-sued/

A Teacher’s Guide to Copyright and Fair Use

. Edutopia; George Lucas Educational Foundation. 

https://www.edutopia.org/article/teachers-guide-copyright-and-fair-use

learn how copyright law applies to curriculum and teaching materials

Curriculum & Copyright