I was bored with all the spam comments, so I decided to install reCAPTCHA. reCAPTCHA is a simple and very effective captcha that is easy to install on almost any platform including self-made sites, blogs and forums. It help very much to protect a site from spam-bots, and you don't need to create any captcha by yourself. All you need to do is to insert the reCAPTCHA code in two places, and it will download everything and will check if the data entered is correct. In addition, this captcha can generate sound that will be very helpful for blind people.

How can you do it for youself. You put reCaptcha's Javascript-code into your form, insert your public key, which was given to your when you registered, in two places. Then upload a reCAPTCHA library to your host (for example, for php this library). And paste the data checking code with the private key in your PHP-script.

How it works. When the page is loaded, reCAPTCHA automatically downloads an image with two words on it that user must enter into the field below. The data then sent to the PHP-script and the checking code detects whether the entered data is correct or not. After that you can whether display an error message or send the user somewhere.