NFT art pieces have an associated file that can be copied but the (nft token, public key) pair on the blockchain is unique, where the NFT token is created with

NFT art pieces have an associated file that can be copied but the (nft token, public key) pair on the blockchain is unique, where the NFT token is created with a public key associated with the artist. Your copy of the associated file is just a copy of the file. You cannot associate another public key with the nft token. As far as we know this is the only reasonable and foolproof way to define digital ownership, digitally.