QuickCaptcha provides CAPTCHA functionality to any website running on a PHP-enabled web host. The graphic image below is easily read by humans, but not so easily by computers. This makes it difficult for someone to implement an automated mechanism to use resources that integrate this feature.
QuickCaptcha allows you to specify string length, allowable characters, color contrast, and several kinds of geometric obfuscation elements.
Knowledge of PHP is not strictly required, but it might be helpful when adjusting the parameters in settings.php so as to avoid syntax errors.