You could do it to public domain art. Maybe set yourself up a shell business, 'NFT Certification Enterprise', and offer your official NFT for each object, with

You could do it to public domain art. Maybe set yourself up a shell business, 'NFT Certification Enterprise', and offer your official NFT for each object, with a guarantee you be generating only one NFT for each object. Deceptive, but not fraudulent. It's not very different than selling overpriced and numbered collectibles.