An often confusing but important concept to understand when mounting stereo images is the Stereo Window. Any object (even the image frame itself) that exists in both left and right images holds a place in space from the viewer. Because of this, the most natural viewing experience is to have scene being viewed behind this virtual window created by the image frame. The "image frame" is the physical black box (Black in this example) that surrounds each image.
you want to avoid is a "Window Violation". A window violation exists
when objects which come in front
of the window are cut off by the window. This is a situation which
cannot occur with a real window
Stereo Window set so that everything is behind the window
Stereo Window set at infinity (everything in front of the window)
Stereo Window set in front of the presenter (the guy with the gun)
A Through The Window Example will come soon.