How does the original owner confirm they own the thing before it gets logged in the blockchain though? I think that's the hard part. The conversion of ownership record from real life to blockchain.
That is not relevant. NFTs do not include ownership of anything else than the record in the ledger. You don't have any intrinsic copyright or other kind of ownership to the token, or to any linked monkey jpegs, by just having the NFT.
(if they do - they do it outside blockchain, what makes blockchain part quite pointless, beyond Ponzi part)