[nathan_hui]

So the general answer is you need to write an algorithm that figures out where on the image the center of the rectangle is, and use that to determine the amount to turn.

The hard part is writing that algorithm. There are a bunch of solutions, none of which are simple. You could use the NI Vision libraries, or you could include OpenCV with your robot project. You could write your own image recognition algorithm (SAD, threshold, SSD, etc.).