@shuro Это кстати даже на сайте CC написано:

CC uses the definition of free cultural works at Freedom Defined to categorize the CC licenses. (Freedom Defined is an open organization of free culture advocates and researchers; the definition was developed by its community as a parallel to efforts such as the Free Software Definition, to have a standard for defining Free Culture.) Using that definition, material licensed under CC BY or BY-SA is a free cultural work. (So is anything in the worldwide public domain marked with CC0 or the Public Domain Mark.) CC’s other licenses– BY-NC, BY-ND, BY-NC-SA, and BY-NC-ND–only allow more limited uses, and material under these licenses is not considered a free cultural work.

https://creativecommons.org/public-domain/freeworks/