Why not just put a LED next to the camera that is also connected to the camera power supply. If the light is on, you know the camera is on. Same should go for any microphones. Best would be to have a physical switch that cuts power to camera and microphone.
I've heard there were occasions when hackers activated camera even without triggering LED next to it. I agree about HW switch.
Why? Because any user can see if the tape-over-the-camera is in place, or if the camera is pointed back down into the internals of the keyboard. But the average user cannot know for sure how an LED light is wired. Furthermore, in worst case scenarios a user might not quickly notice the LED has been switched on, or the LED itself might 'burn out'.
Should be part of privacy standards. For example, a retailer could refuse to sell a laptop that didn't conform to the standard wiring of interface devices and make a point to include this in marketing. I suppose there is a valid point that spying malware could turn on the camera, grab a few frames then turn it off so that the light flashes for less than a second. That would limit the amount of useful data collected. As for the light burning out, the most likely failure mode for LED would result in an open circuit which would mean no camera. LEDs however have typical lifespans greater than 100,000 hours.