What exactly is an NFT?
The most common NFT standard on Ethereum is ERC-721, where each NFT is identified by a unique tokenId.
An NFT records which address owns that token ID. It does not automatically grant copyright to the image; what you can do with it depends on the project's licensing terms.
Transferring and trading NFTs on Ethereum requires paying gas with $ETH . The current price is 2245.33.