Note the final image where you say 'NO' in your comment works with the addition of a Trigger delay (sorry I missed that).
This will ensure the loaded image is pushed into the Freeze, and that any updated Picture is also updated.
This method with the freeze is what I have been using for years (we didn't have GLSL at that time), I don't know if there is any performance benefit?
It does seem the default GLSL is the easiest approach :)