You could disable your webcam by unloading the driver for the webcam.
The procedure on my Samsung P510 with Debian Wheezy was as follows:
1. Find out details about your webcam, e.g. the name. In my case I did:
$Bus 001 Device 003: ID 0ac8:c326 Z-Star
$Microelectronics Corp. Namuga 1.3M Webcam
So we found a name: Namuga
2. Find out which driver operates this webcam:
$dmesg | grep Namuga
$uvcvideo: Found UVC 1.00 device Namuga 1.3M
In this case the name of the driver is: uvcvideo
3. Check whether the driver is actually loaded:
$lsmod | grep uvcvideo
The driver should appear.
4. Unload the driver manually:
modprobe -r uvcvideo
5. Check whether the camera is now disabled. Try to start an application that uses the webcam. In my case I have a application called "cheese". I start this "cheese"-thingy - and it reports "no device found". Wonderful!
6. Disable your webcam permanently. Become root and enter in /etc/modprobe.d/blacklist.conf:
As i said, this was successful on Debian Wheezy.