As an additional feature against scripted attempts to break through the Moodle registration system, it is proposed to adopt an optional CAPTCHA element on the registration form.

CAPTCHA supposedly stands for "Completely Automated Public Turing test to tell Computers and Humans Apart", which is a highly forced acronym for the word "Capture" with an Aussie twist to it

There are two main solutions available in PHP, with various advantages and disadvantages:

1. PEAR's HTML_QuickForm_Captcha element with the Text_CAPTCHA library (http://pear.php.net/package/Text_CAPTCHA)
2. reCaptcha (http://www.recaptcha.net)

Pros and cons of the PEAR package:
+ It already has a quickform element ready for use
+ It can generate visual input in several formats, including images, numbers and figlets (ASCII letters)
+ Not language-specific

• Still in beta stage
• Some areas of the code are patchy at best
• No audio version

Pros and cons of reCaptcha:
+ Widely used and supported
+ Has an audio version

• Only in English
• Image generation is dependent on recaptcha website (internet connection required)