When you buy an NFT for potentially as much as an actual house, in most cases you’re not purchasing an artwork or even an image file. Instead, you are buying a little bit of code that references a piece of media located somewhere else on the internet. This is where the problems begin. Ed Clements is a community manager for OpenSea who fields these kinds of problems daily. In an interview, he explained that digital artworks themselves are not immutably registered “on the blockchain” when a purchase is made. When you buy an artwork, rather, you’re “minting” a new cryptographic signature that, when decoded, points to an image hosted elsewhere. This could be a regular website, or it might be the InterPlanetary File System, a large peer-to-peer file storage system.
Clements distinguished between the NFT artwork (the image) and the NFT, which is the little cryptographic signature that actually gets logged. “I use the analogy of OpenSea and similar platforms acting like windows into a gallery where your NFT is hanging,” he said. “The platform can close the window whenever they want, but the NFT still exists and it is up to each platform to decide whether or not they want to close their window.” […] “Closing the window” on an NFT isn’t difficult. NFTs are rendered visually only on the front-end of a given marketplace, where you see all the images on offer. All the front-end code does is sift through the alphanumeric soup on the blockchain to produce a URL that links to where the image is hosted, or less commonly metadata which describes the image. According to Clement: “the code that finds the information on the blockchain and displays the images and information is simply told, ‘don’t display this one.'”
An important point to reiterate is that while NFT artworks can be taken down, the NFTs themselves live inside Ethereum. This means that the NFT marketplaces can only interact with and interpret that data, but cannot edit or remove it. As long as the linked image hasn’t been removed from its source, an NFT bought on OpenSea could still be viewed on Rarible, SuperRare, or whatever — they are all just interfaces to the ledger. The kind of suppression detailed by Clements is likely the explanation for many cases of “missing” NFTs, such as one case documented on Reddit when user “elm099” complained that an NFT called “Big Boy Pants” had disappeared from his wallet. In this case, the user could see the NFT transaction logged on the blockchain, but couldn’t find the image itself. In the case that an NFT artwork was actually removed at the source, rather than suppressed by a marketplace, then it would not display no matter which website you used. If you saved the image to your phone before it was removed, you could gaze at it while absorbing the aura of a cryptographic signature displayed on a second screen, but that could lessen the already-tenuous connection between NFT and artwork. If you’re unable to find a record of the token itself on the Ethereum blockchain, it “has to do with even more arcane Ethereum minutiae,” writes Ben Munster via Motherboard. He explains: “NFTs are generally represented by a form of token called the ERC-721. It’s just as simple to locate this token’s whereabouts as ether (Ethereum’s in-house currency) and other tokens such as ERC-20s. The NFT marketplace SuperRare, for instance, sends tokens directly to buyers’ wallets, where their movements can be tracked rather easily. The token can then generally be found under the ERC-721 tab. OpenSea, however, has been experimenting with a new new token variant: the ERC-1155, a ‘multitoken’ that designates collections of NFTs.
This token standard, novel as it is, isn’t yet compatible with Etherscan. That means ERC-1155s saved on Ethereum don’t show up, even if we know they are on the blockchain because the payments record is there, and the ‘smart contracts’ which process the sale are designed to fail instantly if the exchange can’t be made. […]”
In closing, Munster writes: “This is all illustrative of a common problem with Ethereum and cryptocurrencies generally, which despite being immutable and unhackable and abstractly perfect can only be taken advantage of via unreliable third-party applications.”