Abstract: A method of tracking a user's toothcare activity comprises receiving video images of a user's face during, e.g. a toothbrushing session, and identifying, in each of a plurality of frames of the video images, predetermined features of the user's face. The features include at least two invariant landmarks associated with the user's face and one or more landmarks selected from at least mouth feature positions and eye feature positions. Predetermined marker features of a toothcare appliance, e.g. a brush in use are identified in each of the plurality of frames of the video images. From the at least two invariant landmarks associated with the user's nose, a measure of inter-landmark distance is determined. An appliance length normalised by the inter-landmark distance is determined. From the one or more landmarks selected from at least mouth feature positions and eye feature positions, one or more appliance-to-facial feature distances each normalised by the inter-landmark distance is determined.