Love the technological aspect, hate the practical implications. Any part of any screen can be a camera. Good luck covering that with a post-it.
I can only imagine placing another matching camscreen face to face onto the source one and sending what it sees to a trusted camera-incapable display. But then there is a lot more practical questions and implications..
Not buying invasive shit?
Won't happen? Think smartphones. Even if you don't have one, everyone around does, with all the consequences.