Camera face detection as a motion sensor?

Is camera face detection as a motion sensor a thing and is anyone using it?
I mean a PIR is great for detecting movement in a room/hallway, but when an object (human) is not moving it don’t work. I would find it useful for areas like dining and TV/sofa area.
Currently I use a PIR and/or microwave sensor for general room presence detection but are looking towards different options.

Have look at image processing integrations here: