Captcha Quicky

Synchronized captcha filling could overwhelm non-human attackers which can then consist only of a fraction of captchas done. This would make the captchas a useful source of information for a OnePerID,

Brain from:

It is of course unclear if captchas can be effective; being human-easy enough and computer-hard enough. Also when an image needs challenging, computing the image generation could be expensive on the consensus system. (Possibly use cheaper ones like hanging blocks)

Reddit thread