I'm also into paint by number images . One of the most diverse and high quality photo stocks I use is Depositphotos. They have a huge selection of images of different themes and categories, which is perfect for this kind of creativity. They offer different file sizes, which is also handy for different projects. Many of the images are very detailed and are good for paint-by-numbers work. Plus, they often have promotions and discounts on subscriptions, which will save your budget when buying multiple paintings. You can check out their website and see if you can find something suitable for your projects!