NFT - what is actually stored on the block chain to represent the digital asset?

Question

According to Wikipedia's entry on NFT the minting process "creates a copy of the file recorded on the digital ledger as an NFT". Is that literally true of Ethereum based NFT for example? For some reason I was under the impression that what is actually stored inside the blockchain is the cryptographic hash of the underlying digital asset, and possibly a reference to the file's location, not the actual file itself. I guess it's easy enough to store the whole file when it is a jpg, or a 30 second video clip, but if you wanted to represent say "The Godfather" as an NFT, that would really bloat the blockchain if the entire film in 4K (about 11Gb?) had to be saved in the block.

Cacomistle

Answer 1

It is in fact hash of the image file, URL of an off-chain resource, or sometimes just a simple ID with no other data.

Take this random NFT token for example. The contract address is 0xd0e7bc3f1efc5f098534bce73589835b8273b9a0 and the token ID is 339.

If you call the function tokenURI(uint256 tokenId), it retrieves data from a mapping mapping (uint256 => string) private _tokenURIs.

The string value for the ID 339 is https://metadata.thetwentysix.io/cryptocats/339. And yes, it is a (off-chain) JSON file that contains link to the actual image https://cryptocats.thetwentysix.io/contents/images/cats/339.png

Restore

Thanks I thought so. Somebody should update the wikipedia entry. – Cacomistle

Wikpedia fixed! – Cacomistle

Just for clarity, there is no requirement about what sort of data might be saved in the NFT to link the token to the digital asset? ie. it could contain any of hash value, uri, or maybe even nothing? – Cacomistle

No requirement - at least on the Ethereum network under the ERC-721 standard which is considered to be the original NFT standard. It even explicitly states that "The metadata extension is OPTIONAL". The metadata interface implements the tokenURI() function that usually returns link to an external resource. – Restore

rightclick. save as. stolen. YoU WoUlD NoT FuNgE a ToKeN – Padraig