[faserx]

NFT only exists inside a specific smart contract operated by someone within some specific rules implemented in the contract. If the smart contract is seriously built, in order to "control" the NFT cloned as an "exact" copy of it, the copier has to control an exact "copy" of the smart contract where the NFT resides. The only way I see to achieve this is to know the private key of the owner of the original smartcontract or of someone who has the power to operate it. It follows that if they control the "exact" copy of the smart contract in an "cloned" blockchain (forked or crafted) they also control the smart contract in the original one. At that point the problem wouldn't be the "copies" but the "original" NFT. If they instead craft a copy without crafting the original smart contract, that would be easily spotted. Your nyan cat besides being unique, has also an "origin", the smart contract, and that can be easily being verified. The same applies if someone creates "another" nyan cat inside the same blockchain. That would reside on some other smart contract and easily spotted as a copy.

[jobigoud]

I think the point of the OP is that you need a central authority to define which copy of the contract is the one with the "authentic" asset.