In his recent post on sextortion as cybersecurity, Benjamin Wittes rightly points out that every webcam should have a physical cover or off-switch. I want to add an additional technical point: Even barring a cover, how the camera's indicator light is designed can make a huge difference. The so-called RAT community, those who take over computers to claim "slaves," (both for sextortion or just for their own perverse entertainment) are often very concerned about the webcam light, since it will tip off their victims that they are watching.
A lot of webcams are simply bad: the light is controlled by software, making it trivial to configure the webcam not to illuminate the light. Others can be better. The previous Apple webcams (circa 2013) were almost right in this respect: Apple connected the green LED to the camera's reset line so the LED needed to be on for the camera to work because otherwise the camera would just reset itself. At least, that was the theory. Unfortunately, you could reprogram the camera chip to ignore the reset line.
Once someone discovers how to disable a light, the knowledge can quickly spread through the underground. For not only is sextortion internet-scale sexual assault, but it is highly democratic. Most perpetrators are using off-the-shelf tools, after all.
Because of this fact, Ben's physical disconnect switch really is the best option. Not only is it highly effective, but it is intuitive. Users understand what an "off switch" does, something key to good security. We'd still need to beware that designers may cheat: so many "switches," like the one controlling the ringer on my phone, are simply another input into the computer, rather than a physical disconnection. And unfortunately there are no real effective ways for a user to know the difference.