There are two important qualifications to copyright restrictions for instructors: The Classroom Use Exemption, and the TEACH Act
Copyright law places a high value on educational uses. The Classroom Use Exemption (17 U.S.C. §110(1)) only applies in very limited situations, but where it does apply, it gives some pretty clear rights.
You can show a lawfully obtained movie or image or project a page from a book for teaching purposes in a live, face-to-face classroom with your enrolled students. No specific type of work is excluded from this exemption. Instructors could read aloud from copyrighted text material, act out a drama, play or sing a musical work, perform a motion picture or filmstrip, or display text or pictorial material to the class by means of a projector. Anything you perform or display must be from a lawfully made/obtained copy.
This does not cover online teaching. See the TEACH Act below to learn more about copyright restrictions for online classes.
The “Technology, Education and Copyright Harmonization Act,” commonly known as the “TEACH Act,” was enacted by Congress on October 4, 2002. It is a full revision of Section 110(2) of the U.S. Copyright Act. Its provisions enable educators to use copyrighted materials for distance education, with certain restrictions.
Although the TEACH Act outlines additional resources available for the online instructor, showing films or videos is still restricted to limited portions.
The Act allows instructors to show the full performance of a nondramatic literary or musical work or display the following types of materials:
Instructors may only display "reasonable and limited portions" of dramatic works. Use only the portions that are necessary to make a point. Instructors in face-to-face classrooms may use these works in their entirety.
Instructors may not transmit or display instructional materials without permission or licensing which students, or their educational institution, are commonly expected to purchase, such as: