1. A method for constructing a three-dimensional, 3D, face model, comprising: detecting, by a computing device, a plurality of landmarks of a face, and their locations, within each of a plurality of image frames; generating, by the computing device, a 3D model of the face from a 3D model of a neutral face, in view of detected landmarks of the face and their locations within a first one of the plurality of image frames; and adjusting, by the computing device, the 3D model to track the face in subsequent image frames, successively adjusting the 3D model in view of detected landmarks of the face and their locations within each of successive ones of the plurality of image frames, wherein adjusting comprises fixing inter-person shape variations, and considering only intra-person expression variation, when successively updating the 3D model in view of detected landmarks of the face and their locations within successive ones of the plurality of image frames.