What you need is premium version. As premium user you
will have full control over access to your script. There are
multiple options for distribution, so you can can allow access
for 1 user/computer only, or to several users/machines.
It is all covered in onlina control panel for premium users.
The module cannot be turned on while you are running the program.
You can use Captcha Custom module or an extension of any Captcha Solving Service to use
