Necessary Series Disclaimer: I am not a lawyer. The information presented in this series is based entirely on my experience as a creator and curator.
Right around the time I was finishing up Alice’s Adventures in Wonderland, I was watching an Extra Credits episode (I was a bad researcher and did not note the video’s URL.) where they used one of Tenniel’s illustration right next to a Disney clip. It made me wonder: How does anyone determine whether or not a movie or television show is in the Public Domain?
The obvious (to me) answer was: They’d go by the current copyright laws and the last known clear copyright holder.
The actual answer, it turns out is far more complicated, simply because of the changing nature of copyright law (although being unable to identify who holds the copyright free and clear also causes headaches. This is such a thorny issue, in fact, that there is no official list of movies or television shows in the Public Domain, and most legal sites who have made such an attempt or consulted on a site trying to make such an attempt have included a note that those looking to use a movie or television show thought to be in the Public Domain should consult with a lawyer.
Some movies have legitimately come into the Public Domain, their copyrights expiring according to the copyright law of the time. Any television show thought to be in the Public Domain (because major revisions to copyright law in 1976 and 1989 have really muddied this matter) are potentially in the Public Domain because the copyright was renewed improperly, dropping the show into the Public Domain, or because there was no copyright symbol on the show. (This is a great quick reference on the tip of this iceberg.) Interestingly, some shows are only partially eligible for Public Domain because some of their episodes contain elements that are still copyrighted.
Really, I think looking at how copyright laws have affected movies and television is a really interesting study in both copyright law and how it affects artifacts over time.