ok but how will i get my arduino to read the computer?
Well, you can have the webcam and the computer on board the robot, or use some wireless serial interface (like Bluetooth, Xbee, etc.) to communicate with a desktop computer. In this case, the webcam should be wireless too, if you want to mount it on the robot.
Or you can get a CMUcam and mount it on the robot and have Arduino talk with it on the UART.