Joon Woong Lee et al. 1995 : Robust and effective real-time visual tracking is realized by combining the first order differential invariants with stochastic filtering. The Kalman filter as an optimal stochastic filter is used to estimate the motion parameters, namely the plant state vector of the moving object with the unknown dynamics in successive image frames. Using the fact that the relative motion between the moving object and the moving observer causes the deformation, we compute the first differential invariants of the image velocity field. The surface orientation and the depth estimate between the observer and the object are computed based on these first order differential invariants. We demonstrate the robustness and feasibility of the proposed tracking algorithm through real experiments in which an X-Y Cartesian robot tracks a toy vehicle moving along 3D rails.