NFT is like a label which is attached to in item - for ex. image.
There are standard erc-721 smart contract templates to generate an NFT.
Some of the templates include a function to store a link to the item on the blockchain.
This smart contract can be deployed on one of the several ethereum bockchain instances - ethereum, binance smart chain, polygon…
Most NFT marketplaces do the job of deploying the smart contract and storing the link to the item on the blockchain.
But a person can do it themselves.
NFT is not the item.
The same item (image) can have multiple NFT addresses (labels) on the same blockchain or on different blockchains.
