[Alan Anderson]

If you can track the rectangles, than you can find the x coordinate of the target you want to aim at. If your camera is mounted such that it turns with the turret, you need to establish what screen coordinate the turret actually is aiming at. Then you can find the difference between the desired coordinate and the tracked one, and use that to turn the turret and make the two values the same.

Do you understand that high-level description?