Oooh boy I just found that something that's fairly niche but might be helpful or fun to a few people.

The website Fanatical where I buy quite a few steam games has a bundle of 40 coloring books with 200 pics each with included commercial rights on any derivative works.

Sounds like a good place to start if you want to get into coloring, making adopts or ychs, or just you're in need of a random image for like a painting in the background of an pic.

https://www.fanatical.com/en/pick-a.....artbook-bundle