I don't see any mention of 'camera' or 'face' in this article, interesting tho it is...
ah I misread OP, thought we were discussing something else.
As far as I can tell, this claim is completely false. Do you have a source for this claim?
That's terrifying. Is it known/clear to the user that the camera is on?
No, but some recent versions of Android allow you to disable camera access to specific apps. Unfortunately, always ask every time isn't enough of an option. Simply don't use apps that refuse to work without the camera permission.