system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If certain images such as van Gogh's "The Starry Night" are in the public domain, how are reproductions able to be sold?

Do posters pay anything to use an image in the public domain? 
How does public domain relate to other types of media like books and audio? 

Thanks in advance friends.
gpt
Public domain means the opposite of what you're imagining, when something is in public domain it means anyone can freely use it for any purpose (including profit) without needing to pay anyone. Anyone can take a book or movie or song that's in public domain and sell it without needing to pay royalties or fees.