Reliable segmentation and motion tracking algorithms are required to achieve gesture detection and tracking for human-machine interaction. In this paper we present an efficient method for detecting and tracking moving hands in sign language video frames. We make use of the geodesic active region framework in conjunction with new color and motion forces; color information is provided by a skin color model, while motion information is derived from the optical flow field. Extensive experimentation indicates that the proposed algorithm behaves sufficiently well for gesture detection and tracking.