hey roseenglish, what kind of game is it?
are you using a 3d gaming engine? or is it more of a web browser type game? once you can elaborate a little more, we can help you out a bit more...
if the game is using a 3d gaming engine, most of those have the capability to create the cell shading look for you, for example check out the video game "thirteen" here's a link
XIII-the-game Official site
but even a lot of the textures you see there are just hand painted.
...the more we know the more we can help you out