http://enxx3bysve3s7deur2pz6fdyezucnxotvr257byhbvtmjxq52tmbdnyd.onion/operate/3.html
And while we experimented with them, they just caused annoyance to mods, users, and us. We decided to implement our own solution, this is now we are working towards. On the long run captcha's still can be added somehow, since they have to be solved, they still cost to the attacker.