The same as with any other intellectual property (books, movies, songs): buy the legally enforceable copyright. As in "right" and "copy".
PS: I'm immensely interested in the process of creating a digital image. It's actually pretty tricky and technical, to apply all those filters in right order and with right settings. I would buy a recording of how the digital art was created.
Except the legally enforceable copyright is just that: legally enforceable. The legal system is what creates a financial incentive to own the rights to something as opposed to just copying it in some way that might constitute IP theft.
With NFTs, there is no legal benefit to actually owning the NFT.
PS: I'm immensely interested in the process of creating a digital image. It's actually pretty tricky and technical, to apply all those filters in right order and with right settings. I would buy a recording of how the digital art was created.