You can do the exact same thing with a blockchain NFT - there's absolutely no difference in terms of outcome. Each "sale" generates a unique digital signature NFT because the public key of the person buying is incorporated as part of the cryptographic signature.
Every sale is on the blockchain, so if somebody creates multiple sales of the same item, it would immediately be visible. Of course it depends on the implementation, how do you identify an object?
Leonardo could still create one NFT saying "this is ownership of my painting of the woman that always looks at the beholder" and another saying "this is ownership of my painting "Mona Lisa" and it would perhaps not be immediately clear that they are the same painting.
Nevertheless, that is the "minting" problem and not the "spending" (or transfer) problem.
Edit: HN does not allow me any more replies at this point, sorry.
I want to add, while I suppose in reality people would settle for specific blockchains (like you can identify the Bitcoin blockchain), I can see a problem for NFTs. As long as there is not the ONE blockchain for NFT ownership, it would be difficult to prevent somebody "selling" the same thing on different NFTs.
Even if the seller says "xyz is the official blockchain", it does not really solve the problem, as they could just say that several times for different blockchains. It does not actually add new information (signing something and putting it on blockchain xyz is equivalent to signing something, putting it on blockchain xyz, and saying "xyz is the official blockchain for my NFTs").
Not sure if you understand how public key cryptography works?
The artists says "this is my key" to their public key. Then they can use their key to sign things, and people can verify the signature because they can check that it belongs to the public key, which the artist has publicly announced.
Obviously you need a way to identify the real artist. For example if they put their public key on their official web site, it would be a pretty good indicator.
People also used to create chains of trust with public key infrastructure. Maybe you trust Bob, and Bob trusts Alice, and Alice has personally met the artist at Burning Man and verified their key there.
Or you go to the government and let them provide a register of identities. In any case it is a separate problem.
If you can't verify the artist, don't buy the NFT, or only buy it at a discount, accounting for the risk. Forgeries are a problem with physical works of art, too.
> Obviously you need a way to identify the real artist
Thats the point though. Nothing about the blockchain has anything to do with this part, and this is really the only part that matters.
So, once again, my point stands. The private key has nothing to do with identifying the real artist. Instead, it is something else entirely that identifies the real artist.
> on their official web site
So then the official website is what is doing the identifying here, of what the real art it. Not the blockchain. It is the artist themselves, saying "This art is the real one", not cryptography.
It is not proof of work, or proof of signed private keys. Instead, it is proof of "official website".
> In any case it is a separate problem.
It is the only problem that matters. The actual way to identify the real artist, separate from the blockchain, is what is actually doing all of the heavy lifting here. The private key isn't doing anything on the important part.
But you can't prove ownership of the actual art, with an NFT.
You can only prove ownership of that specific crypto transaction, which might be just a fake NFT, or duplicate.
There is nothing about crypto that actually proves it was the "real" NFT, or real art.
You need something else to actually prove that you own the "real" piece of art or NFT.
> Not identifying creators
If you are unable to identify creators then you are unable to prove ownership, because that NFT could just be a fake one, or even a duplicate that the creator has issued many times without you knowing it.
With crypto alone, you'd only be able to prove that you own something that might just be a fake or duplicate, and anyone can make as many fakes or duplicates as they want, so that's not really proving ownership.
You are conflating several issues. Yes, a creator presumably would have ways to cheat the system, for example by selling the same thing on different blockchains (as mentioned elsewhere). But eventually they would be revealed to be frauds and presumably the worth of their creations would plummet.
To verify the identity of a creator is a solvable problem, though, and is also yet another issue than the "sell it multiple times" problem.
