In this paper we address the problem of real time object tracking in complex scenes under dynamically changing lighting conditions. This problem affects video-surveillance applications where object location must be known at any time. We are interested in locating and tracking people in video sequences for access control and advanced user interface applications. Here we present a real time tracking method suitable for human faces. A Skin Probability Image (SPI) is generated by applying a skin hue model to the input frame. Targets are located by applying a modified mean-shift algorithm. To obtain their spatial extent, error ellipses are fitted to the probability distributions representing them. The hue model is unique for each target and it is updated each frame to cope with lighting variations. This technique has been applied to human face tracking in indoor environments to test its performance in different situations.