Add Latest Overlay Image (Alt+V)

After you have used 'Add Overlay Image', a copy of the overlay is retained in memory.
This may be applied to the current background-image or any subsequent background-image by using the 'Add Latest Overlay' option.
It is also useful when repeatedly adjusting the stereo-depth of the background image.
As described in the 'Add Overlay Image' section, the fastest way of doing this is to adjust background, 'Add Latest Overlay' image (assuming it has first been loaded) and if not satisfactory, delete the overlay and repeat the sequence.