Capture image from video streaming by D5M camera

My frame size is 320x240.

I have Altera UP IP cores with streaming protocol. I inserted one line buffer(size 320)in between by building a custom component.

So, every pixel passes through the line buffer. Now, when i want to click the image, I will be storing the next 320x240 pixels coming to my line buffer.

Please correct me if I am wrong.

Now, when I press the button to click, the current pixels in the line buffer could be any, throughout the image. So while storing the next pixels, I need to know the their locations so that while displaying them back, I can give it to appropriate location in pixel buffer memory.