According to my understanding ERC721 smart contracts hold a list a "NFTs/owners" the same way ERC20 smart contracts hold a list of "owners/token balance".

NFT are digital assets that can be uploaded to those contracts and "assigned" to a given owner, that can later re-assign them to another owner (selling the NFT).

What is then preventing someone from serializing the same NFT and uploading it multiple times into the same smart contract? or What is preventing someone from uploading the same NFT to multiple ERC721 smart contracts? or even worse, what is preventing someone from uploading the same NFT to different blokchains?

If that is indeed possible then there is no actual guarantee that NFTs are unique and ownership would not mean anything...

I am very probably missing something...

3 Answers 3


Strictly speaking, an NFT is a unique ID inside a unique NFT contract address. And yes, they are assigned to owners very similarly compared to ERC20.

The NFT contract has a certain address in a certain blockchain. In theory the same address can be generated in another blockchain, but to be precise, you should talk about for example Ethereum NFTs. Inside the contract each unique NFT has an ID. So one ID can be owned by only one address.

All of the other data is basically just extra sugar and/or metadata. For example the NFT image is just some image uploaded somewhere, and the NFT contract has a pointer to the image URL for that unique ID.

So, yes, you can duplicate the NFT contract, utilizing exactly the same data (also metadata), but it has a different contract address.


I agree with @Lauri's answer and actually have been wondering the same questions during this NFT hype.

However, just to extend the topic, NFTs are not new and can be used for a number of different use-cases besides collectible jpg's that anyone can download from a public IPFS. Below are just 3 examples:

  • A gaming platform can trade with NFTs representing lands, weapons, cars, etc and they will only be valid from the original smart contract, so other forks or replications to that contract won't be usable within the game.

  • NFTs can represent real assets, such as a properties, and retail investors could be buying portions of that asset to receive a monthly reward from its renting (kind of fractional investing to assets that are normally too expensive for average investors).

  • Tickets to access events, allowing also to resale those tickets in a traceable way avoiding counterfeit.

There are a lot of use-cases, and the current hype of selling digital art at insane prices is generating a bit of misunderstanding about the real potential of non-fungible tokens.


An important distinction here is "an NFT" versus "a unique digital representation of an artwork."

Like Lauri says, each NFT is technically unique. But we don't yet have a way to ensure there is only one NFT issued against a piece of art.

Someone could issue multiple NFTs against the piece of art on the same smart contract, or across multiple smart contracts, or multiple cryptocurrencies.

For now, we're solving this like the physical world. After selling a painting, artists could theoretically repaint the exact same one, creating a duplicate.

Artists don't do that because it would devalue their work and reputation. The same restrictions apply for NFTs.

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