Upload folder cosmo into /ext and configurate and activate the CAPTCHA on your ACP
Attention: To use this CAPTCHA you need to surf to peoplesign:). Register there (for free). Create your private key and the CAPTCHA configuration of your like. The free version only has a peoplesign:) watermark when the CAPTCHA is shown.
This Extension is a conversion of the CAPTCHA mod by peoplesign:) for phpBB 3.0. Big parts of the code are from the guys from peoplesign:) and not from me.