Works such as movies or sound recordings may contain many underlying works, such as musical sound tracks, painted illustrations, or other works. There has been a disturbing trend by some copyright owners to assert protection in an element of a public domain work. For example, the film It’s a Wonderful Life fell into the public domain because of a failure to renew copyright. For years, anyone was free to copy and sell the movie on videotape. However, a production company recently acquired rights to the musical sound track that is used in the movie. That sound track is not in the public domain. The copyright owner of the sound track can now prevent anyone from copying the music, thereby effectively stopping anyone from copying the film (unless the sound track is removed). Multilayered works can create confusion when trying to determine public domain status.
Usually you don’t have to be concerned with this type of legal maneuver as it is only used in connection with popular and older multilayered works such as classic films. It would be difficult, if not impossible, to apply this procedure to a public domain book or painting.
Public Domain Works That Are Modified
Modifications to a public domain work may be protected by copyright and cannot be used without permission. A famous example used in many copyright classes is the artist who paints an elaborate hat and mustache on the Mona Lisa. Even though anyone is free to copy the image of the Mona Lisa, the modified image (with mustache and hat) is protected under the artist’s copyright.
Works Protected by Trademark Law
It is possible that a work may not be protected by copyright, but is still protected by trademark laws.
Works Protected in Other Countries
Before 1978, most countries had different periods of copyright protection than the United States. As a result, many works that are public domain in the United States are still protected by copyright in foreign countries and vice versa. Therefore, you may have to research public domain status in each country in which you plan to publish your work.
Often an author creates a work by selecting various public domain components and grouping them together. If the selection, coordination, and arrangement of the material is unique, it will be protected as a copyrightable compilation.
Works First Published Outside the U.S.
The copyrights of some works first published outside the United States have been resurrected, removing them from the public domain. As a result of international treaties signed in the 1990s, public domain works that meet certain qualifications are now protected. (For a detailed discussion, see The Copyright Handbook, by Stephen Fishman (Nolo).)