It can be basically anything you can think of, in theory at least. I quickly googled what you are asking and it seems it's already being done:
https://www.instagram.com/nftoilpaintings/?hl=en
You can think of an NFT as a sort of proof of ownership that resides on a decentralized ledger.. like a book that has pages spread out all over the internet, and different people out there have keys that can unlock whatever they are storing in this book. When you buy an NFT, you are buying one of these keys and your key unlocks something specific in that book. The question of "What is stored in the book?" can be answered in many ways since you can pretty much store almost anything there, the only limit being how many bytes whatever you are storing takes up. The more you store, the more you will have to pay in transaction fees in order to store your data on the ledger. So a lot of NFTs are links to art that are stored elsewhere (If I understand this correctly), since a link doesn't take up much space at all.. and I think that's why a bunch of NFTs are pixelated and small.. but I could be wrong about that.
So it depends on what you are trying to accomplish, I think. Personally I feel that if this technology survives, it will be used for various things, and one of them will be a sort of proof of ownership. So, if you own an expensive piece of art, or some antique collectible, or some unique lego set, or anything of value.. When you buy it, it could one day come bundled with an NFT (key) that is essentially your proof of ownership OR proof that you are the original creator. This ledger stores all these details in a public way so that anybody can look it up and see who originally minted it and who currently owns it. Meaning that if you were ever to want to sell your collectible, the buyer might want proof that it isn't a fake, and you'd shown him the NFT. This is basically the same thing as a certificate these days comes with collectibles that is signed and stamped, etc. except that in this case the technology 100% proves that your certificate is genuine.. i.e. can't be faked. I am not sure exactly how you tie the NFT to the physical object and prove that they are connected, but I assume there's ways of doing that, since some sports card and other collectible companies have started using NFTs for this purpose.
Some companies are using the technology to bundle NFTs with a ticket for some event. So.. I have a friend who went to a rave and as part of that she got an NFT (a slightly more expensive package I think). This NFT gave her access to some things at this event, such as a VIP tour of something, I can't remember the details. It also gave her access to some other stuff outside of this event, I think a discount on a rave cruise or something like that? So.. in your scenario, you could in theory do something like this if you ever have an exhibit where your art is shown. How exactly would be up to you and your imagination, pretty much. I've seen some sports teams bundling NFTs with season tickets and regular tickets as well, and IIRC it gives you access to some extra things at the stadium or whatever. So basically.. that sort of approach
So yeah, NFTs aren't always weird pictures of slightly different apes that you can buy as digital art. The technology is a lot broader than that. The apes is just one implementation of it, and it's caught on for whatever reason.
So.. as of now, you have these options:
1. Mint your oil painting as an NFT in an attempt to sell digital collectible versions of your art. So basically.. You could paint something on a real canvas and then take a picture of it and mint 100 copies of it as sort of digital collectibles for your fans to own. Why would anyone want to own a digital version of your painting? I dunno but some people like to collect things. If you are the one who painted AND minted the NFT, this would be reflected on the ledger, and this could excite some collectors *shrug*. If you end up being famous one day in theory these 100 digital copies could be one day worth something, which is perhaps why some people might be tempted to buy one. It's basically like buying trading cards, except you are really buying keys that unlock these digital pictures that live on a ledger. SO, in theory you could do this as a way to promote your art maybe, I'm not really sure. It probably depends on your target market. From what I understand a lot of artists who dabble in this space will hold events to advertise the "NFT drop", and that creates a buzz and puts more eyes on their art, which is in part why they do it. Some of them are looking to make money, but not always. Some NFTs can be bought for $1 or less. So.. Just in this 1 point there's varying reasons why you'd be tempted to do something like this
2. Mint your oil painting as a sort of proof that you are the original creator and that you own it, and not put up the (one) NFT for sale. Then if one day somebody rips you off, you have an easy way to show that you are the creator and owner. I have a friend who is doing this with some of his original art - some of it was stolen and somebody was making $$ selling it online.. It took some doing to get it taken down, the marketplace wanted definite proof that the art is really my friend's creation. After this hassle he decided to simply mint all his original art so that next time it will be a lot easier to prove that he's the artist who created it, and owns it. So yeah, you don't need to put up your art for sale as an NFT. You can just mint it for other reasons and specifically indicate that it's not for sale. There's carbon neutral blockchains like WAX and other cheap blockchains that allow you to do this on the cheap, so you don't have to spend a lot of money minting your art. on WAX you can mint for a couple cents, I think.
3. You can use your oil painting and insert it into a sort of algorithm that generates similar art somehow, and then mint 100 different versions of it. This is more complicated and I can't find an example of somebody doing this, but I remember reading about something like this. So basically.. You could take your original painted art, take a picture of it, and then convert it to different things somehow. Maybe one of them will be pixelated, another one uses inverted colours, or whatever. Then you can sell these digital variants of your original art and hold an event, in an attempt to put your eyes on your art. If you get a following, in theory that would mean that more people would be tempted to buy the actual physical art. So .. this is similar to 1. but a bit more complicated.
Just some ideas. I'm a bit under the weather today and am on tylenol.. No idea what I caught, hpoefully not the rona.. but.. either way I'm a bit out of it, so I hope my post makes sense
I'm not an NFT expert by any means, but I feel that I have a decent grasp of what the technology is and how it can be used. And I do know people who are using it as a sort of proof of ownership like I said. I feel that this usage of NFTs will only get more popular (but I could also be wrong). IMO the people who are selling apes for $200,000 each or whatever are exploiting the human nature of wanting to collect unique things, and the fact that there's people out there have more money than they know what to do with.
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