When I test your form I'm able to successfully register, then receive the email and verify my email address by clicking on the link. When I click on this link I'm taken to your users_Confirm page with a message thanking me for verifying my email address and a link to login.
If users are having a problem with getting the emails it may be due to the delay and emails are not being sent immediately. If the users are having problems with the CAPTCHA graphic and cannot enter the details correctly you should update the CAPTCHA settings in your global file to make it more readable. You can adjust the size, the text color, the background color, the font, and the amount of 'visual noise' you see. We have a document on making these adjustments and others in the global file. Here is a direct link to it:
You should make some adjustments to this CAPTCHA to make it more readable for your users. You can do some testing of it yourself by deleting your user from the db and registering as a new user.