Fighting spam: personalized question at signup?

I feel like if I could add just one personalized question at account creation, a bit like a captcha, but a fixed question with a non-checked answer, it would help me fight spam a bit.

The question could be like “Que comptez-vous faire sur notre instance ?” (yes it’s a french community), or “What’s the name of the current president of our fundation?”, or whatever make sense for the community using the given instance.

The answer could be displayed in /admin/users/{user_id} for admins to review them when in doubt abount an account…

Maybe this could be tweaked to serve a larger purpose by allowing a set of questions instead of just one, allowing admins to implement very personalized captcha, adding questions from time to times, and removing old ones. I don’t feel like answers should be checked automatically though.