How to create an additional sign up step? User need to upload image upon sign up before they are approved to browse or post

I have setup a private community for a particular software that is in widespread use.
However, I want only the administrators of the software to be able to sign up (not users).

So I would like to ask the administrators to upload an image of the software showing their administrator privileges in order for me to approve them to be able to browse or post a topic.

Any suggestion as to how to implement this?

This plugin can help