It would still be possible for a bot to do. You can't have the shape requirements be to precise or you would annoy customers that do the shape but don't get it perfect. What about players with disabilities that make that fine control of a mouse harder? You don't need fine control to play WoW. You would need to indicate some way of shape and place to draw. The place to draw if not random could easily be figured out by a bot. You could have the client send a chat string (or any other kind of text) for what shape to draw or a bot could easily parse it.
You don't stop bots by making it cumbersome for normal people to play. You'll still have bots but just more user attended bots.