Years ago there was an article about 2008 era Mac laptops that could enable their cameras without turning on the LED. I believe the camera firmware was read from RAM on boot. So they just intercepted that. Since then they redesigned the hardware to tie the LED to the sensor camera source. AFAIK Apple hasn't published any official documents on this. I, too, would be curious if it could be hijacked by only taking a still image or modulating the power, but I haven't of anyone actually do this.
Their laptop cameras haven't changed in like a decade. The only change was making it physically thinner to match thinner screens. The image quality actually got a little worse.
Wasn't there an NSA tool leaked that would turn on the camera, grab a picture, and have it off again before it would be lit up?
It would be technically possible.