Copyright Circular 22: How to investigate the copyright status of a workExplains several approaches to investigating the current copyright status of a work including examining the copy of the work, searching the Copyright Office records, and contacting the U.S. Copyright Office for assistance.
U.S. Copyright Office. Circular 22: How to Investigate the Copyright Status of a Work. Washington, D.C.: U.S. Government Printing Office, 2013. Web.