You also don't need to have one processor do every thing. Use a WiFi cam mounted on the 'bot. Link the cam to the PC and have the PC do the image processing and send instructions to the 'bot. Lookup robotics - horse and rider.Mark
I am no expert at this, but the company I work for was using image processing hardware in their machines over 20 years ago(!). Isn't the Arduino (or a few of them connected together) "strong" enough to do what was done by hardware 20 years ago?
Pauses thread here for a moment and rewinds.....Is this really an image processing issue or just light following?