[LaurentS]

Not exactly answering the question, but I recently used aliexpress.com and their captcha system is super easy: it shows a sliding button like the one to answer a call on a phone. The prompt just asks you to slide it to validate your input. Not sure how it works, but it sure is a much better UX than when I have to spend 3 minutes identifying for hydrants. Maybe we could make a FLOSS version of it?

[renewiltord]

The common recaptcha is just a "check box to prove you're human" if Google knows you even slightly otherwise.

[hexandcube]

But is that good for accessibility?