blue-captcha

This captcha is best, or i’d say better – the only one i could find through all wordpress catalog that actually stopped all those infinite flow of spam on my site. This plugin’s captcha is fully configurable, means you can make it as easy or as hard as you want, though default settings work good

Highly configurable. The best captcha plugin to install.

known problems: 1)a lot of pictures are difficult to read even for human 2)on incorrect loginn try it clears login text field and it is not user-friendly