Copyright

There are four factors in a Fair Use evaluation, each of which can weigh a use in favor or against being a fair use. Most often, the 1st and 4th factors are the most relevant 

The four factors

1. the purpose and character of your use
2. the nature of the work you are using
3. the amount and substantiality of the portion used
4. the effect of your use on the potential market

The Purpose and Character of Your Use

• Uses such as teaching, research, scholarship, criticism, or commentary are favored by fair use
• If a use is "transformative", meaning the new use of the work transforms the original work into something entirely new to make a new point or for a novel purpose, it is highly likely to be considered fair use

The Nature of the Work

• Highly creative works, such as visual art or music, is more heavily protected by copyright
• Less creative works, like scholarly articles, are less protected by copyright

The Amount of the Work Used

• To be considered a fair use, the amount of the copyrighted work used without permission must be only as much is needed
• This can vary from using an entire work to just using a portion

The Effect on the Market

• If a use is likely to create market harm for the author or otherwise harm sales, it is less likely to be considered a fair use