Dear Kumar,
Mathworks provides a toolbox (the Computer Vision System Toolbox) that lets you track the object. When you click on 'Camera Calibration' you can find information how the camara has to be calibrated such that distances can be calculated.
If for example it is given that the object moves towards the camera, the change in the size of the object (which can be calculated with MATLAB) is related to the frontal velocity of the object. If hereby the size of the object is known, the frontal speed could be calculated. (v=ds/dt, where ds can be expressed by the area change of the object)
Good luck! Christiaan
