It really depends on what captcha you use. Obviously, there's no such thing as a botting-proof captcha (just like there are no such thing as a site which is impossible to exploit, unless there are no user interaction at all). However, some captchas are easy to exploit (like SolveMedia) and others need a more creative bot developer (like the AreYouAHuman captcha).

We will of course keep a keen eye on the market, and always try to stay ahead of any possible bots or exploits that might appear.