Studying high-res digital paintings is the same as looking at a traditional painting in a museum. You can start to reverse engineer how it's made and learn a lot without asking any questions. What's more fun, is that sometimes you'll find something you probably shouldn't have. For example, when Destiny was first announced, I found the actual file that was used to create the promo poster. Overall, I love finding concept art and zooming in really close. You can start to distinguish what brush they use, if it has photo textures or not. Take a look through some of my favorites here. I'll keep it updated as I find more.