Q. What is public domain?

"Public domain" refers to works that are no longer protected by copyright. To determine whether a work from a U.S. author has entered public domain, you'll need to know the name of the author, the title of the work, and the year of its first publication. To take a simpler approach, assume that any work published in the United States after 1923 is under copyright.

Check for copyright - http://www.copyright.gov/records/