What is ERC-721?
ERC-721 defines the ownership and transfer interface for distinct tokens, commonly known as NFTs.
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What does ERC-721 define?
ERC-721 is the standard that defines the ownership and transfer of distinguishable tokens on Ethereum. It is widely used for assets known as NFTs (Non-Fungible Tokens). While units of the same token are interchangeable in ERC-20, each token in ERC-721 has a separate identity number within the contract.
For example, token number 125 and token number 126 in a collection are separate records. The fact that they belong to the same collection does not mean they have the same image, characteristics, or market value. To definitively identify a token, the network, contract address, and token ID are required together.
What do you get when you buy an NFT?
The standard allows for tracking which address a specific token belongs to. However, this ownership does not automatically grant the copyright of the image, permission for commercial use, or ownership of a physical object. If such rights exist, they must be separately explained in the project’s license and related agreements.
The image itself is not always kept on the blockchain. The token record may contain a link to a file on another server or in distributed storage. Where the file is stored, whether the link is changeable, and the maintenance of access are issues separate from the token standard.
The distinction to note when granting permissions
You can grant transfer permission to a marketplace for a single NFT, or you can authorize it to manage all your NFTs in a contract. These two approvals are not within the same scope. If you see a phrase like “approve for all” in a wallet request, understand that the transaction is not limited to only the piece you want to sell at that moment.
ERC-721 compliance does not prove the authenticity of the collection or the reliability of the seller. Fake collections can use the same names and images. Verifying the official contract address along with the transaction history on a marketplace is more informative than relying solely on the image.