Buying an NFT doesn´t give you any rights over the picture, you don´t own the copyright, all you have is a certificate of authenticity. Although some NFT have attached terms and conditions and they could give you the copyright. For example, this meme sold for half a million dollars, there are maybe four million memes with that photo, but the buyer has the original one, the one that started it all, and he has an NFT to prove it.