A green light appears beside the camera when it's active.
There is no way to activate the camera without the green light. Big Brother is not watching you.
If you're still paranoid, at least go paranoid in style:
If you're not in high school, own your computer (rather than having it loaned to you by a company, university, or primary school), and do not work for the government, then no one wants to spy on you anyway. If you can't come up with a good reason why someone would want to spy on you, then no one is spying on you. I can understand taking precautions to ensure that your computer is safe (which it already is, out of the box), but believing that someone wants to watch you through your webcam or record your voice while you're computing is taking it a bit to the extreme.