A method for determining a state of vigilance of a driver in a vehicle using a predetermined image-analyzing algorithm. The method especially includes a step of executing the predetermined algorithm on the generated sequence of images in order to detect a series comprising at least one movement of the head of the driver, a step of determining the speed and/or the amplitude of each identified movement and of the dynamic and static periods of the head of the driver, a step of detecting dynamic and static periods of the head of the driver and of measuring the frequency and duration of each period, and a step of determining a state of vigilance of the driver from the speed and/or the amplitude determined for each identified movement and from the frequency and duration of each detected period.