Many of the works that are not protected by copyright are considered to be in the public domain. Some works are not copyrightable (See "What is Not Protected" under the "Copyright Basics" tab). Many government publications are in the public domain. Works whose copyrights have expired are also generally included in the public domain, although "orphan works" (those works for which the copyright owner is unknown or unlocatable) are not currently included in this group. To assist in determined whether copyright protection has expired for particular works, Peter Hirtle, senior policy advisor in the Cornell University Library, has created the "Copyright Term and the Public Domain" chart, published by the Cornell Copyright Information Center and shared under Creative Commons Attribution License 3.0. http://copyright.cornell.edu/resources/publicdomain.cfm
Use the Digital Copyright Slider to determine copyright duration.
The Technology, Education and Copyright Harmonization Act of 2002 is an exception to the Copyright Act set forth in Section 110(2). Generally, it allows teachers and students at accredited, non-profit educational instititutions to transmit performances and displays of copyrighted works under specific conditions. All of the conditions of the exception must be met in order for the TEACH act to be applicable. Thus, it may be helpful to consider the Fair Use exception as more applicable, depending on the circumstances of your proposed use.
If you choose to apply the TEACH Act exception to your proposed use, we strongly recommend using these guidelines from Louisiana State University's TEACH Act Toolkit to determine whether the TEACH Act may be applicable in your case.
FAQs regarding TEACH from the American Library Association: http://www.ala.org/advocacy/copyright/teachact/faq
The Digital Millenium Copyright Act of 1998 significantly altered certain portions of copyright law. Areas addressed include prohibition of the circumvention of access-limiting technology and limitations for vicarious and contributory liability, especially concerning online service providers. Because the DMCA is lengthy and complex, the U.S. Copyright Office has provided a summary of the legislation here: http://www.copyright.gov/legislation/dmca.pdf
As noted elsewhere in this guide, reading the law is the best way to develop an understanding of its content. The DMCA affects several parts of Title 17 of the U.S. Code, so it may be useful to compare the summary with the full text of Title 17, available from the U.S. Copyright Office here: http://www.copyright.gov/title17/
You may also find useful the Association of Research Libraries' collection of information related to DMCA: http://www.arl.org/pp/ppcopyright/copystatutes/dmca.shtml