In determining whether a particular use of a copyrighted work is permitted as fair use, the courts will evaluate the use in light of four factors.
"It’s important to understand that these factors are only guidelines that courts are free to adapt to particular situations on a case‑by‑case basis. In other words, a judge has a great deal of freedom when making a fair use determination, so the outcome in any given case can be hard to predict." [from: Stanford University: The 4 Factors]
- The purpose and character of the use.
- Are you using the work as a basis for parody or for criticism? That would more likely be considered fair use.
- Does your use of the original transform it, to add expression or meaning? Was value added to the original by creating new information or new insights? It can be difficult to determine what is transformative, and the degree of transformation. In general, the more transformative it is, the more likely to be fair use.
- The nature of the copyrighted work.
- Is the original work creative or factual? Is it published or unpublished?
- Fair use is more likely to apply to factual published works. Creative or unpublished works probably require permission.
- The amount and substantiality of the portion used in relation to the copyrighted work as a whole.
- Are you taking a small or large portion of the original work?
- A small part is more likely to be considered fair use, while a large amount would not be. Be careful about using a small part that is the "heart" of a work, such as the identifying musical phrase, or "giving away" the core of the work in a critique; these could be an infringement of copyright.
- The effect of the use on the potential market or value of the copyrighted work.
- Is your use likely to create a larger market for the original work? That tends to fall under fair use.
- Could your use of the work be a substitute for the original, causing the original owner to lose revenue? That will require permission.