What's not covered by Copyright?

Although most information is protected by copyright, there in an exception: works within the public domain which can be reproduced or used by anyone. Yet even though you can use these materials for free, you still must credit the author.

Here are some examples of public domain sources:

Public Domain Sources:

Publications of the U.S. Government
U.S. laws and other publications of the Federal government, the U.S. Constitution
Copyright has been waived by the author.
  Software called freeware
Works on which the copyright has expired
Works by William Shakespeare