Thanks for your reply @balaji.ambresh.
I understand what is going on in the attached image. My point is whether we are using the 16x16 image or the 28x28 image, the window size being implicitly used is 14x14. What if I want to scan the image in 8x8 sections for example. One reason we might want to use a smaller window size is that the car might be far away in the image appearing smaller. We would want a smaller window size to narrow down the position of the car.