A common misconception about NFTs is that they are stored directly on the blockchain. Generally, this is not true.
IPFS stands for Interplanetary File System, which is a decentralized peer-to-peer file sharing system.
Rather than host the media natively, NFTs typically including links that point to files stored on IPFS services such as Pinata or Infura – meaning that the media used to represent an NFT is hosted on a separate decentralised network.
IPFS services offer many tools that NFT creators can utilise, such as the ability to add, remove or change the media relating to an NFT.
There is no way to guarantee that the data of an NFT will be forever untouched. As a rule of thumb, it is best to buy from projects that use a trusted IFPS service, especially if you have any concerns about its authenticity.
There are some NFT projects where the art is minted directly on chain, such as Autoglyphs by Larva Labs, and TwelveFold by Yuga Labs