I used 3D art for all the game images for the same reason. On average, it probably takes me about 2 hours per picture right now but that really depends. The program is DAZ3D and is free but all the art packs cost money and can easily cost you thousands to get enough assets to do much with. It's partially why the game has slowly gotten better and more full with other characters. I could slowly add more people into the game with better hardware and after more people donated to the project. You can check out Daz though if you want. There's also YouTube videos on how to use it. Very steep learning curve though if you've never done it before. I'm pretty rough at it