There are two NFT standards: the first and most used - called LRC721 - has the characteristic of uniqueness, that is to say that a work sold through this standard is equivalent to a unique piece. Two examples of this NFT can be found in Cryptopunks - the first ever project of works with an NFT -, consisting of 10 thousand faces/avatars created algorithmically with all different characteristics, and the more recent Cryptokitties, a 3.0 version for those who are allergic to cats, but love them platonically. The second standard - LRC1155 - has the feature that a contract is worth multiple tokens. In this second case, it is as if the ownership of the work is divided among several people, becoming the equivalent of a work made in a limited-edition series. An example of the use of this standard can be found in the auction of Andy Warhol's series 14 Small Electric Chairs (1980) - auctioned by the platform Maecenas and the crypto art gallery Dadiani Syndicate in 2018 -, in which almost half of the ownership of the work was sold.
The NFT is nothing more than an electronic certificate with an encrypted code, and the signature of the artist attesting to the uniqueness and ownership of the work. If until a month ago the sale of NFTs belonged exclusively to the world of crypto art, this sale marks the official entry of this type of "digital object" into the traditional art market. In a screenshot of Beeple you can read the triumphant comment: "Surely this sale will mark the beginning of a new chapter in the history of art, that of DIGITAL ART". As already anticipated, the auction has exceeded all predictions, marking an absolute record in the sale of works of art in general: with $69,346,250 (paid with the cryptocurrency Ethereum), Beeple becomes the third highest priced living artist after Jeff Koons and David Hockney.
As mentioned, Nft stands for non-fungible token. More or less, it means that this token is unique and cannot be replaced with its equivalent. A $10 bill is fungible, because if you exchange it for another $10 bill you have the same value in your hand. A figurine of Micheal Jordan autographed by him is instead non-fungible, because if you exchange it with the same figurine of Jordan, but not autographed, you have in your hand a completely different object.
This is perhaps the metaphor that best explains what a NFT really is: the digital equivalent of an autographed sticker, which therefore assumes a different value from all the others. A NFT is not the digital work of art you have purchased, but the token uniquely linked to it that proves it is yours. An NFT is the certificate of ownership stored on the blockchain (which, thanks to its characteristics, makes it impossible to counterfeit, duplicate or steal it).
In case a metaphor more related to the art world is useful, we can rely on the words of Dannie Chu, CEO of MakersPlace (NFT buying and selling platform): "There are hundreds of thousands of prints and reproductions of the Mona Lisa, but since they are not the original created by Leonardo, they are worth much less. The same principle applies to NFTs: you can copy and paste an image or a video, but the original, digitally signed by the artist, is what has value."
It's like owning an original Picasso of which an exceptional forger has created hundreds of absolutely indistinguishable copies. The fact that to the human eye there is no difference between the original and the copy does not make the original any less valuable. In the case of the set of Beeple's works sold by Christie's, therefore, it is not important - for the purposes of market value - that each individual creation is visible on the website of the digital artist himself. What matters for the investor is to possess an NFT that contains the high-resolution file of the work and the artist's digital signature.