Hello,
Firstly I must say your extension is very useful for my page, but when I tried to add captcha code to the registration form it didn't work. The captcha was displayed but not considerated at all. Off course I suspect it is a session problem, but I am not really sure, since I am just a beginner in joomla and programming. I learned that your extension somehow overrides original joomla user module/component, so I assumed that I should put the form to display captcha in components/com_k2/templates/register.php and that the code will be processed, I have changed components/com_user/controller.php (I have attached some pictures, so that you can see what exactly I have changed!) I also wrote at the top of both files. I did as the instructions on the page says: www.phpcaptcha.org/documentation/quick start-guide/
And yes I have tried some other plugins and they worked fine, but I already have this captcha on my page (and I would not want to confuse the visitors with million different captcha styles...), so It would be much appreciated if you could help me to work this out. Oh and I have k2 V2.4.1...

With best regards