I think Unsplash was kind of like this until they were bought by Getty Images. Really loved they're way of presenting ads.
On a personal note, I tried getting into ads for one of my personal projects (a map of recycling points for my hometown), but Google declined my application because it doesn't have much content on it — though it's kind of absurd because people use my web app, to find locations on the map, not read content. I ended up not doing ads for now, and keep receiving "buy me a coffee" donations.
In a way it is, but I haven't done anything in the past few months, so it kinda faded. Made $250 from "buy me a coffee" this year, and yeah, I paid taxes on them.
I basically send an invoice for each tip I receive. Talked a lot to my accountant about this, and she said that if I don't invoice the people sending me these tips, I'm doing fraud, and can pay huge fines once I get caught. I think only as an NGO you're allowed to receive tips w/o paying taxes on the amount. I have an LLC, so I have to invoice every income.
It sounds like you're in Europe? They require invoices for everything there.
If you're in the U.S. though...you need to find a new accountant. You don't need to invoice every transaction. It certainly is advisable, for accounting/auditing purposes (much easier to track and verify income), but it's not mandated.
On a personal note, I tried getting into ads for one of my personal projects (a map of recycling points for my hometown), but Google declined my application because it doesn't have much content on it — though it's kind of absurd because people use my web app, to find locations on the map, not read content. I ended up not doing ads for now, and keep receiving "buy me a coffee" donations.