[cooper12]

IANAL. Fair use doesn't have a strict definition and depends on a bunch of factors that would be considered in a court:

* the purpose and character of your use

* the nature of the copyrighted work

* the amount and substantiality of the portion taken, and

* the effect of the use upon the potential market.

(https://fairuse.stanford.edu/overview/fair-use/four-factors/)

You certainly can include copyrighted content in commercial art, for example if it's a single second of a video, the main subject of discussion (such as in a review), a small portion of a complete work (like a quote), and more. Non-commercial use could still affect the potential market for an original (such as by outselling it or defacing it). So a lot of it depends on how much you're using, how you're transforming it, and how it affects the original.