Works in the public domain may be used freely without the permission of the former copyright owner. According to the U. S. Copyright Office, a work of authorship is in the public domain if it is no longer under copyright protection or if it failed to meet the requirements for copyright protection. Many U.S. federal government documents are not entitled to copyright protection under U.S. law; therefore, images within many government publications and web sites are free to use.
Which items are in the Public Domain in the U.S.?
Helpful websites about when works enter the public domain: