Copyright ownership today in the United States lasts for the life of the author plus 70 years. For anonymously created works and works made for hire (that is, created for an employer) copyright lasts for 95 years from publication or 120 years from creation depending on which one is shorter.
Determining whether works created before 1978 are still protected by copyright can be a complex undertaking. Depending upon when a work was created, it is subject to different requirements regarding copyright notice, registration, and renewal, as well as different copyright terms. For example, before 1978 U.S. law required that works be published with a notice of copyright to receive protection. Failure to comply with this requirement would result in the work being in the public domain. The Copyright Term and the Public Domain, a guide to copyright duration created by Peter Hirtle at Cornell University, is a useful resource for starting to research a work's copyright status.