Adding CAPTCHA Protection to Your Website

This guide explains what CAPTCHA protection is, when to use it, and how to implement it in various programming languages.

What is a CAPTCHA?

A CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart) is a test designed to determine whether a user is human or a computer. The most common CAPTCHA is an image showing obscured letters or numbers. Users must type the correct sequence to access website content or submit data. Automated bots usually cannot read these images, helping prevent misuse of your website’s resources.

The following image is an example of a common type of CAPTCHA:

When to Use CAPTCHA Protection

Consider adding CAPTCHA protection to any web page that processes user-submitted data, such as:

• Forms (email, comments, registration)

• Surveys or polls

• Pages that accept file uploads or downloads

• Any page that accepts user input

CAPTCHA Implementations

There are several free and open-source CAPTCHA implementations depending on the programming language your website uses.

PHP

Some popular PHP CAPTCHA solutions include:

• Securimage: Easily add PHP-based CAPTCHAs. More info: phpcaptcha.org

• captchas.net: Provides CAPTCHA implementations for multiple languages including PHP. More info: captchas.net

• Google reCAPTCHA: A widely used CAPTCHA service. General info: google.com/recaptcha, PHP integration: developers.google.com/recaptcha

• Text_CAPTCHA PEAR package: Allows creating custom CAPTCHA implementations in PHP. More info: pear.php.net/package/Text_CAPTCHA

Python

• captchas.net: Also provides a Python implementation. More info: captchas.net

More Information

For general information about CAPTCHAs, visit Wikipedia: CAPTCHA.