I guess you could transfer ownership on nostr. For example, if someone paid me 345,635 and sent me a message with the amount, I could announce they now own this jpeg on nostr by creating a signed message that says they own it.

This is simmilar to the way ownership of money rocks was.transfered on the island of Yap. The rocks were there for everyone to see. Everyone knew who owned the rocks.

Information longs to be free however. This "ownership" does not come with any property rights. Intellectual property requires a court system. If someone uses this jpeg I own without  paying me, I doubt I could sue for copyright infringement,  but I don't feel like these laws are useful in the electronic age anyway.