What’s the point of buying an NFT if can just download the picture?
The answer to that question lies in the concept of NFTs. Yes, you can, in fact, simply download whatever picture you can find on the internet. However, it’s next to impossible to determine who owns the original, except for the owner of the NFT, which means that the NFT’s value rests in the hands of its owner — and no one else.
Also don’t forget that picture is just a representation of the NFT. You own not the JPG itself, but the utility behind it.