Moving object detection using D5M/DE1-SoC

My design just use Avalon Streaming to transmit video from camera to VGA. It just transfer the pixels to VGA as it get them from camera.

question: How does camera work?? Assuming camera is giving a 30fps video. I can think of two cases:

1. Is it some thing like it captures one whole frame at once and transmits it pixel by pixel. And while it is transmitting, it doesn't capture the other frame (so the captured pixels are unaffected while camera module is transmitting them). And as soon it completes transmitting the previous frame it captures another frame and starts transmitting it. In this case, every frame is buffered in camera module first and then transmitted.

OR

2. It captures the frame pixel by pixel and transmits it simultaneously. In the case, the whole frame is not buffered in the camera module.

Issue:

If it is the first case, the moving object should be visible (movement may not be that smooth) because it is just discretely capturing what is visible.

Also, In this particular case, I tried keeping the whole frame total white and the object as black. And in between the streaming protocol, their is a small logic which check for the presence of black pixel and raises a flag if it found one. So when object is still or moving really slowly I can see that flag raised but if i increase the speed slightly the flag is de-asserted. That means their is no black pixel in the whole frame. How is that possible.

I doubt it has to do something with the camera specs like exposure time/shutter speed. Please suggest.