A hand washing monitoring system (1) comprising a camera (2), a processor (4), the processor being adapted to receive from the camera images of hand washing activity. The processor analyses mutual motion of hands to determine if the hands mutually move in desired poses, and if so, the durations of the patterns; and generates a hand washing quality indication according to the analysis. The processor extracts information features from the images and generates feature vectors based on the features, including bimanual hand and arm shape vectors, and executes a classifier with the vectors to determine the poses. The processor uses edge segmentation and pixel spatio-temporal measurements to form at least some of the feature vectors.