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:
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.
PHP
These are some of the numerous CAPTCHA implementations available for PHP:
- The Securimage script enables you to easily add PHP-based CAPTCHAs to a website. If you need more information, please visit http://www.phpcaptcha.org.
- The captchas.net service provides CAPTCHA implementations for several languages, including PHP. If you need more information, please visit http://captchas.net/sample/php.
- Google provides the reCAPTCHA service. If you need information about reCAPTCHA, please visit http://www.google.com/recaptcha. For specific information about implementing reCAPTCHA with PHP, please visit https://developers.google.com/recaptcha/intro.
- If you are a programmer and would like to write your own CAPTCHA implementation, you can use the Text_CAPTCHA PEAR package in PHP. If you need more information, please visit http://pear.php.net/package/Text_CAPTCHA.
More Information
If you need more information about CAPTCHAs, please visit http://en.wikipedia.org/wiki/CAPTCHA.
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