The centralised marketplaces themselves (like OpenSea) are able to and might try to police duplicate NFTs, or other counterfeit near-matches. I'm not actually s

The centralised marketplaces themselves (like OpenSea) are able to and might try to police duplicate NFTs, or other counterfeit near-matches. I'm not actually sure if they actually do. But on the blockchain itself, the NFT is just a smart contract (bit of code, bit of data) that knows it's current owner, it's name and a URI pointing at the image. There zero mechanism preventing duplicates. Hell, it's such an unregulated market that the NFT might be based on a custom smart contract with a backdoor that allows the creator to steal it back at any time.