PeterH:
That begs the question - what is the point of trying to use the Arduino for this type of project?
What would you suggest? I know that Arduino (+ WiFi Shield) and an IP camera would solve my problem however the hardware of the IP camera really and truly can already do what I am doing with the Arduino. For example I found an IP camera which I can tilt and rotate; if the hardware of this IP camera can already do this then it can also manage another motor to move a pair of wheels.
However I do not know what kind of boards these IP cameras have inside. I guess what I am looking for is something that fills the gap between Arduino and RaspberryPI (I think RaspberryPI is too much for this type of project).