Method and system for monitoring a vehicle driver includes an optical imaging system that obtains images of the driver, and a processor coupled to the optical imaging system and arranged to analyze the images obtained by the optical imaging system to locate a head of the driver in the images and monitor the driver's head or a part thereof over time. The processor also determines, based on the monitoring of the driver's head or part thereof, whether the driver has lost the ability to operate the vehicle. A reactive component is affected by the processor's determination that the driver has lost the ability to operate the vehicle, and requires action by the driver to indicate regaining of the ability to operate the vehicle or exerting control over the vehicle to slow the vehicle and bring it to a stop.