The Association of Research Libraries provides a brochure for faculty and teaching assistants called Know Your Copy Rights: What You Can Do. Some information is out of date.
The Resources for Teaching Faculty – Frequently Asked Questions page contains an excellent six-step checklist for making a “good faith” judgment of fair use of copyrighted material. The FAQ is divided into two sections: one for the traditional (face-to-face) classroom, and the other for the online/course management hosted classroom.
Fair use allows for the use of copyright-protected works for educational purposes, as well as for commentary, parody, news reporting and research.