One of the reasons NFTs are on the blockchain and not elsewhere is that the blockchain is immutable and decentralized. This means that if you buy an NFT today , you expect the content to never change and not be controlled by anyone. I will show you that this is not the case for the large number of NFTs in circulation .
Three main ways to store NFT content data
As of today, every NFT you create on OpenSea is stored on their servers. If you look at the details, you will notice that the metadata is editable.
This can also be confirmed when you look at the URI in the smart contract
This type of NFT is mutable and stored off-chain . This is not an ideal way to store your data, because if OpenSea fails or gets hacked, you will lose your data. The creator can also replace the image with something else.
Some creators also create NFTs and store the files on their website. You will also lose your NFTs if they stop maintaining their website or get hacked . Don't think this only happens to cheap NFTs .
Another way of storage is to use immutable and decentralized off-chain storage like IPFS . Your files are stored on multiple computers, and if one fails, you have a copy elsewhere. The advantage of this is that the same URL will always give you the same file. It is not possible to change the content file without creating a new URL . This means that your NFT will always have the same content, even the creator of the content cannot change it. You can identify it by the prefix ipfs:// .
OpenSea allows you to store files in IPFS , all you need to do is click the freeze button. If you haven't already done so, please do so.
The third way to save data is on-chain . This means your data is stored on the blockchain and is immutable. This was done in the past, but is no longer practical today due to the cost of smart contracts containing large amounts of data. Some developers store some properties on-chain and a lot of content off-chain.
Proxy and URI changes
I looked at the contract and the URI starts with ipfs:// , which means I'm safe, right? In most cases, yes, but I'll tell you, that's not always the case.
Some smart contracts have the ability to change the URI , such as this one.
Your image is probably already in IPFS , which means the address will always return the same content. But if you change the address, the image will also change. The only way to find out if this is possible is to read the source code of the contract.
The last point I want to make is the use of proxies. Smart contracts are immutable, which means you can never change the rules. But what if I told you there was a way to change the rules?
Since you can't change the rules of a contract, they came up with the idea of creating a contract that can be replaced by another contract. You're not changing the contract, you're voiding it and replacing it (which in my opinion is the same as changing the rules). You can buy an NFT and replace your smart contract with something completely different in the future. This is the riskiest type of NFT you can buy . Continuously improving the code is a common practice in software development, but I don't think this should be the case for simple NFT contracts.
Mystery Box NFT
Some artists create NFTs in which you buy a " mystery box " that hasn't been revealed yet, and when it's revealed, you know what you've bought. Revealed NFTs have different values depending on the rarity of their properties.
If blockchains are always predictable, how can random properties be created and reveal NFTs in such a way that no one knows the outcome in advance ?
The strategy people use to do this is pretty simple. You set a URI for the undisclosed file , and after the sale ends, you change the URI to the disclosed file. I don't like this solution because the creator of the contract may choose which NFTs to send to whom.
You can see an example in the MetaBillionaire smart contract.
in conclusion
I have shown you many ways in which contracts can be changed or manipulated, which I believe runs counter to the ideals of decentralized and immutable systems. If you ask me why people create these types of NFTs , I can think of several reasons.
Most people don't have enough knowledge to create their own smart contracts, so they use OpenSea . OpenSea doesn't use IPFS by default , but it can. People with knowledge of creating contracts sometimes want to create ways to update their work. Let's say you bought an image today and the artist decides to replace it with a higher quality image. There are many reasons why they might create mutable NFTs , whether you trust them or not, I'll leave it up to you, but keep in mind that immutable contracts will always be the same as what you bought.