There is significant debate as to whether public domain even exists except through copyright expiry. Such serious claim requires some serious citation. It is

There is significant debate as to whether public domain even exists except through copyright expiry. Such serious claim requires some serious citation. It is certainly not true as stated, since all original works produced by the government are in the public domain regardless of when they were created (e.g., NASA images and many US coins designs.) The first Google result for [public domain existence debate] is your comment. I haven't come across any evidence that any such debate exists, and plenty of sources to support the fact of the existence of public domain (some given by others in this thread.)