Comment spam, guestbook spam, e-mail spam is getting on my nerves. I’m always looking out for the next best thing to protect my web sites from any spam messages. Usually, I protect my web forms using a Captcha (a graphical security code) which needs to be resolved by a real user in order to use the form. Now I’ve found a great free service which allows you to protect information with a graphical code without doing any programming.
reCaptcha  was created by the Carnegie Mellon University. Put their free code on your web site and it’ll display a web form with some scrambled words which cannot be detected by spam robots. They also provide an audio-version for visually impaired people.
Below you’ll see a short example of reCaptcha. Once you solve the Captcha, you’ll see my e-mail address:
reCaptcha also provides plugins for WordPress and Mediawiki as well as sample PHP code if you need to customize the functionality.