For the nieve - capchas will not work. The reason is most all the bots use pixel scanning. It would be very simple to have bots scan the capchas with pixel scanning, then input it into the field. So it will not do anything to stop the bots. Maybe slow it down for a day while the code is written is all. The bots are already doing this for item drops.
A better way is to log the status of a user. if it is on and joining gams 24/7, guess what, it's probably a bot. Seriously if it is running eldritch, shrenk, meph, and andariel 8 hours a day 7 day a week for 8 weeks, guess what... It's a bot.
There are ways for the server to log and detect actions, plus warden. Just use a little common sense.