The Copyright Law of the United States provides legal protection for intellectual property. In your search for information, you should assume that all materials you find are copyrighted, unless the document specifies that it is public domain, which means that it can be used freely by anyone. An information source does not have to be registered with the Copyright Office to be covered by copyright. It is copyrighted as soon as it is created.
The doctrine of "Fair use" allows copyrighted works to be used for purposes such as criticism, news reporting, teaching, scholarship, or research. Fair use generally applies to nonprofit, educational purposes that do not affect the potential market for or value of the copyrighted work. Section 107 of the Copyright Law describes factors to consider in deciding when fair use applies. The issues related to copyright of computer software, digitized images, and other products and sources are becoming more and more complicated. Some have not yet been adequately interpreted by the courts.
Remember that all information sources and technology have been created by someone. Depending on how you use their property, you might have to ask those authors, developers, publishers, etc for permission. To be safe, do not copy anything unless you have explicit permission or a clear statement that the item is in the public domain. Whether an information source is copyrighted or in the public domain, you should cite it if you quote or paraphrase it in your paper or speech.
The United States Copyright Office of the Library of Congress
The web site for the United States Copyright Office of the Library of Congress provides online access to all of the copyright key publications, including informational circulars, application forms for copyright registration, news of what the Office is doing, including Congressional testimony and press releases, our latest regulations, a link to our online copyright records cataloged since 1978, and links to the copyright law and to the web sites of other copyright-related organizations.
Fair Use of Copyrighted Material by Georgia Harper, J.D.
Georgia Harper is considered the foremost expert on copyright among the members of the National Association of College and University Attorneys (NACUA). She is manager of the intellectual property section in the General Counsel's office for the University of Texas System, and a member of the Association of American Universities Copyright Advisory Board. This site includes (for example):
Crash Course in Copyright
University of Texas's Copyright Crash Course includes presentations for administrators, faculty, students, libraries, and university attorneys.