How we can track a single selected object from multiple detected moving objects using single fixed camara?
What kind of an object? If it is a compact object moving in some predictable fashion, you can use the Kalman filter to track based on its motion. If the object has some texture, and doesn't move very fast relative to the frame rate, you can use the KLT (Kanade, Lucas, Tomasi) algorithm to track points on it. If it has a distinctive color pattern you can use a Mean-shift tracker to track it.