Yes, it's free. But we do ask that if you find it useful you provide a link to our website like this.
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.
One feature that makes QuickCaptcha relatively robust is that the code changes every time you refresh the page or guess the code. This presents one problem: If the wrong code is enterred and the user clicks the "back" button to return to the form or if you take them back to the form if they enter the wrong code, most browsers will not refresh the image although the expected number is now different. In other words, the (cached) image is showing an old and incorrect number. You will need to defeat the browser's cache. The meta tags "pragma" and "cache-control" do NOT work.
This normally isn't a really big problem, as you can write failure page in a way that takes them back to the page without using the "back" button, and thus the image should be regenerated. For complete control, you'll need to do some server-side scripting on the forms page that changes the filename of the requested image by adding a random number to it:
Something similar could be done in ASP or the server-side scripting language of your choice.