Fear that your webcam can be hacked is, of course, not completely baseless. Both Windows and OS X allow any program running on the computer access to the webcam without asking for specific user consent, and webcam images often make excellent blackmail material in a time when blackmail is becoming more common, or at least higher-profile.
And while nearly all webcams come with indicator lights that make it easy to spot when they’re being used without your consent, it’s true that they can sometimes be activated over very short, barely noticeable periods. My Macbook Pro’s camera, for instance, does take a few 1-3 frames to warm up 1, but it’s possible to capture 3 frames on the webcam with the indicator LED flashing for just half a second. It’s hard to miss if you’re actually using your laptop, but the camera can just as well be used when the computer is in screensaver mode. In that case, it’s likely that you aren’t paying particular attention to it and won’t notice.
There have also been some reports of webcam lights being hacked: there is a known vulnerability in older macs, for instance. However—to my knowledge—no such reports have been made for more recent Mac cameras, or for other popular camera models, even though there is certainly a large interest towards finding such vulnerabilities. This is a fairly strong sign that such vulnerabilities are rare in general, but the possibility remains concerning.
Yet as with all security measures, safety benefits must be weighted against usability concerns. Just as a computer that has its USB ports disabled and is disconnected from the internet is very safe but seriously less useful (and even then…), disabling your webcam comes with all sorts of small-but-repeated annoyances: you have to remove the tape every time you want to use the webcam, change the piece of tape as it stops sticking, spend time choosing just the right tape, and, admit it, you’ll generally look paranoid. But it’s true that these are all minor problems.
The real flaw in the webcam obstruction analysis is this: an attacker that has access to your webcam certainly also has access to all your files (as well as you microphone, which is difficult to disable and has no usage indicator). When I’m not using it, my laptop mostly remains closed, and when I am using it, well, pictures of me staring at reddit are a lot less juicy than getting access to all my private conversations, passwords, bank account details, or whatever other kompromat my weird colleague/the NSA is trying to dig up on me.
In the end, if you’re already careful about malware in general, I’m not sure taping your webcam will improve your security by any significant amount. If you aren’t, that’s what you should focus on. And if you’re directly targeted by the NSA, probably just burn your laptop?
Picture brightness increases over ~5 frames when the camera starts, making the first few images hard to use. ↩