Copyright holders cannot totally restrict access to their work or restrict the use of it. Section 107 of the U.S. copyright law designates that copyrighted materials may be used under certain circumstances. These circumstances are known as fair use.
Fair use ensures both our ability and our democratic right to freely exchange and transform ideas. If your use is fair, permission from the copyright holder is not required. Specifically, Title 17 of USC §107 states:
In determining whether the use made of a work in any particular case is a fair use the factors to be considered shall include—
Image credit: By Óðinn at English Wikipedia (Transferred from en.wikipedia to Commons.) [Public domain], via Wikimedia Commons. Available at: https://commons.wikimedia.org/wiki/File:Fair_use_logo.svg
How to apply fair use to your situation
Fair use is analyzed on a case-by-case basis. Fair use is extremely important to educators because it allows them to use copyrighted materials in the classroom. Keep in mind that not all fair use is educational in nature and not all educational uses are fair.
To figure out if your intended use of a work is fair, you need to balance the use based on the four factors. If your responses weigh in favor of fair use, then you may use the material without obtaining permission from the copyright holder. If your responses weigh against fair use, then you are best advised to obtain permission for the use. See the Seeking Permission tab for more information.
Here's a handy chart to help you determine whether your use is fair. You might also want to download the Fair Use Checklist created by D. Buttler and K. Crews.
Adapted from Crews, K. Fair use checklist. Columbia University Libraries. Last updated May 14, 2008. Retrieved September 25, 2018 from https://copyright.columbia.edu/content/dam/copyright/Precedent%20Docs/fairusechecklist.pdf
A Fair(y) Use Tale
Below is a brief copyright law primer by the Stanford Fair Use Project. It is compiled with Disney clips. The irony here, of course, is that Disney has played a major role in working to change U.S. law in extending terms of copyright protection on its works. See Sonny Bono Copyright Term Extension Act. So this tongue-in-cheek video pokes fun at Disney's prolific legal actions re: copyright while using the clips to provide instruction on fair use. This video is just over 10 minutes in length.