The Technology, Education, and Copyright Harmonization Act (TEACH Act) was enacted in 2002 as an amendment to Section 110(2) of the Copyright Act. As in the case of fair use, the TEACH Act allows for exceptions to copyright law. "It allows displays and performances of copyrighted works to be transmitted and used for instructional purposes, without permission of the copyright holder, if numerous conditions are met. It complements the so-called 'face-to-face teaching' exception in the copyright law that allows educators to display and perform any copyrighted work - movies, videos, poems - in the classroom without permission of the copyright owner" (Ashely, 2004). For additional information about the TEACH Act, see the following resources.
Ashley, C. L. (2004). The TEACH Act: Higher education challenges for compliance. Educase: Center for Applied Research 2004(13), 1-11. Retrieved from https://library.educause.edu/resources/2004/6/the-teach-act-higher-education-challenges-for-compliance
A work is in the public domain when it is no longer covered by copyright, because the copyright term has expired, the creator has released the work, or the work was never copyrighted. The public then holds the rights to the work and can make use of the image. This means that you can use as much of the work as you would like to support your instruction, research, publication, creative work, etc. without needing permission from the original copyright owner.
Determining if a work is in public domain can be tricky. Consult the following charts for guidance: