How to add CAPTCHA protection to your web site

Last modified: Tuesday November 28th, 2023

This article describes what CAPTCHA protection is when you might use it, and some implementations for various programming languages that you can add to your own website.

What is a CAPTCHA?

A CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart) is a test that tries to determine if a user is a human or a computer. The most common type of CAPTCHA is an image of hidden letters or numbers displayed in a frame. Before accessing website content or submitting data the user must correctly enter a sequence of letters or numbers. Since automated bots usually cannot read these images, they cannot be misusing the resources of the website.

Here is is an example of a common type of CAPTCHA:

How to add CAPTCHA protection to your web site kb captcha example

When to use CAPTCHA protection

Add CAPTCHA protection if your website has any of the following:

  • Forms that process user-submitted data, including e-mail forms, comment forms, and registration forms.
  • Surveys or polls.
  • Pages that accept file uploads or downloads by users.
  • Any other pages that accept user-submitted data.

CAPTCHA implementations

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


These are some of the numerous CAPTCHA implementations available for PHP:

More Information

If you need more information about CAPTCHAs, please visit

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