On a Windows machine, you can open up the device manager, click on Imaging devices, right click on the line for your integrated camera and select disable--do not select uninstall unless you want to completely remove the software that operates the camera.
If you have a parental control filtering program you can also block but, for most families, your first line of defense should be to talk with your kids.
"The message I share with parents is that it's fine if their elementary or middle school kids use a supervised chat room with three or four of their friends, but I wouldn't allow kids to go into unsupervised chat room to chat with people they don't know." Dess recommends you have a discussion with your child even if you're not aware if he or she has used a site like Chatroulette. " If the child says they have used or know of such a site, it might be a good time to talk about an appropriate code of conduct.
You could start with an opening comment like "I've heard about kids going into video chat rooms to interact with people they don't know. If they're oblivious to it, said Dess, "you can just drop the subject." For the time being at least.
Parents beware Parents need to be aware that this service is out there and getting increasingly popular.