Blue Captcha is a WordPress plugin by J. Kokkalis (BlueCoder) and V. Kokkalis that effectively protects your WP blogs from spammers and unwanted persons.
Screenshot of Blue Captcha Image On Register Form
Features:
It can be applied to any of the following : login form, registration form, commentary form or password recovery form
It’s highly customized
It has 7 predefined CAPTCHA difficulty levels to choose from – of course, you can adjust your CAPTCHA settings and create a custom level
The possible CAPTCHA customizations are more than enough
It can apply the same or totally different CAPTCHA settings on login form, registration form, commentary form and password recovery form
It can display CAPTCHA to only non-registered users or registered users
It can preview CAPTCHA image before applying it
It supports 5 different fonts and 5 different background images
It supports single or double CAPTCHA layer
It can display up to 20(!) characters on Captcha Images
It is capable of adding extra drawing (lines, circles, grid, transparent lines) on CAPTCHA image
It is capable of keeping log file which registers all activities concerning user logins, user registrations, user comments and password recovery
It provides blocking options as well
It can export the entire log file into CSV file (Excel)
With the help of log file, it’s easy to track down the IP address of spammers or unwanted persons and ban them for ever
Plugin homepage: http://mybluestuff.blogspot.co.uk/p/blue-captcha.html
Download: http://wordpress.org/extend/plugins/blue-captcha/