I feel like (based on my experience with devs working on captchas) a useful captcha module is more trouble than it's worth. I could enable kaptcha, but it has major flaws too and not my code to make public. It recently proved to be useless against automated spam on another site anyways.

>TPH/PPH
Making them based on PPH doesn't sound like good ideas, there are only organic dumping threads that would increase it