There was an article or post about this about a year ago. Someone was making a device that could be carried on a person and would interfere with the electronics on a camera up to 30ft away. They talked about it being away for celebrities to foil in your face paparazzi or at least the ones using dgital or film cameras heavily reliant on electronics.
What if you could carry a device that did emit an EMP signal that could fry the insides or at least disable a digital camera. Would you be liable for damage to the phtographers gear or could you argue your were defending your privacy?