New User Flood

Actually, now that I think about it. I think Voidious used Asirra to prevent issues on the berrybots wiki. Now asirra is closing down this year, so we can't use that. But there should be some other image based captcha's around.

As we all know, classification is a very difficult AI problem, but is almost trivial for us humans. :)

Usually, it is sufficient to ask what is "2+2", may be in the form "two plus two" so it is not that obvious for a parser. Since, we are fighting attacks not designed against this particular wiki, it will be sufficient. Once, a traitor give the answer to this question to a bot net, we will ask what is 2+3, and so on.

We could just randomize it so it's 17 + 21, and then just tweak the way it is said so it becomes thing likes "one before eighteen plus one past twenty"

Wow, I would not pass such captcha on a first try :). It sounds like the french way to call numbers, which I believe, is not very common.