Copyleft is a play on the word Copyright to describe the practice of using copyright law to offer the right to distribute copies and modified versions of a work and requiring that the same rights be preserved in modified versions of the work. In other words, copyleft is a general method for making a work (text, music, computer programs, Images, etc....) free and requiring all modified and extended versions of the program to be free as well.
Copyleft is a form of licensing and can be used to maintain copyright conditions for works such as computer software,documents, music and much more. In general, copyright law is used by an author to prohibit others from reproducing, adapting, or distributing copies of the author's work. In contrast, an author may give every person who receives a copy of a work permission to reproduce, adapt or distribute it and require that any resulting copies or adaptations are also bound by the same licensing agreement.[From Wikipedia]
If a work is within the public domain, there are no copyright ownership issues associated it.
This is because the work was either never eligible for copyright protection OR, the term of copyright protection has expired.
Therefore, anyone may reproduce, redistribute, or adapt the work and there is no longer a need to seek permission for its use.
On January 1, 2019, a wealth of material fell into the public domain in the US - everything published in 1923. For help searching for this material, check out our HathiTrust guide.
Here are a couple of handy tools to help determine what is in public domain in the U.S. as of this year-
The websites listed here are starting places for your search of free-to-share materials on the web. Other websites may also be helpful, just be sure you know how the original creator intended for their work to be used.
This guide is designed to share information on copyright and related topics. This guide does not supply legal advice nor is it intended to replace the advice of legal counsel.