How does one stop the flickering when one renders still images? I tried to apply a bit of Box Blur(1,1). It's lessens the flickering a bit but not entirely. The flickering is worse in "Pan & Zoom."

Waynevid
Kdenlive 0.7.8 revision 4733
NTSC VGA 640x480
framerate 30000/1001

You need to better describe the problem. I created a project as VGA NTSC. I placed a 2304x1728 photo in it. I played it. No flicker. I rendered it and played the result, and no flicker.
Let me guess that you are doing an animated pan & zoom where I can reproduce a problem, which I would personally not describe as flickering. (When you say "flicker" I think of artifacts typically associated with interlace.) The amount of low-pass filtering required is not a one-size-fits-all deal due to the Nyquist theorem. Try to increase the the blur factor to 2. Oh, and make sure the blur is before the pan & zoom.