Is public domain based on the copyright of the work OR is it based on when the author died OR perhaps it is based on something else?
Basically, how do you know if something is in the public domain?
The Public Domain…intellectual property’s frontier. These are the adventures of those working with no copyright. Their mission: to use pre-existing content, to explore not being sued for infringement, to boldly go where no legal protection has gone before..!
[Insert inspiring theme music here!]
Sigh. If only this question was as simple as putting on a spandex unitard and exploring the galaxy. Unfortunately, it isn’t, and there is no one hard and fast rule for assessing if something is in the PD (Public Domain), and thus available for use without licensing, permission, or any concern about copyright.
So what do you do if you want to work with material you think might be in the PD? You have to analyze it.
A work has several ways of getting into the PD:
1. It lacks sufficient original authorship to have ever qualified for copyright protection. Example: a simple, non-descriptive list of characters in a play.
2. It qualified for copyright but was never protected. Example: a play published in the US in 1957 without a copyright notice.
3. It was once protected, but the protection expired. Example: a play published in 1988 without a copyright notice, and without subsequent registration within 5 years.
All three of these can be tough to assess. There is, however, a great chart maintained by Cornell, that enables some determination related to #2 and #3.
Do you need to assess if something is in the Public Domain? Check out the chart. With the right information about a work (the author/owner, date of publication, and circumstances of publication) it can be used to determine if a work is in the Public Domain. But take care! When working with the chart, make sure you verify every relevant variable. Have someone knowledgeable, or an attorney, double-check your conclusion.
Once you’ve done that, you can voyage to the undiscovered territory, secure in the knowledge that no one can sue you for infringement (based on copyright).
 “The public domain” should not be confused with “copyleft” practices such as Creative Commons licenses, or “Open Source” agreements that authorize use under very light restrictions; such licensing is still based on the underlying property having a protectable copyright.