I remember there was a story saying that it's possible, via software only (due to a "bug" and some "poor" hardware design), to turn on the camera without activating the LED.
It used to be that the LED was controlled by firmware. As far as I know this is fixed now but I haven't proven it myself.
There are leaked schematics of MacBooks online (that unofficial repair shops use) so if you want to investigate this I'd expect it to be a good place to start.
Published in 2013, but describes "the Apple internal iSight webcam found in previous generation Apple products including the iMac G5 and early Intel-based iMacs, MacBooks, and MacBook Pros until roughly 2008".
There are leaked schematics of MacBooks online (that unofficial repair shops use) so if you want to investigate this I'd expect it to be a good place to start.