This example page demonstrates multi layered CSS background images triggered by JS.
The bulb image is on top of another bg image and doesn't appear in the Page Info Media list.

Currently right clicking on them doesn't show any graphic options.
It could work somehow like:
 check right clicked element (innermost not covered, like Inspector does)
  if element has bg images
   loop over sorted bg images, start with most frontal:
    if click was within it's box
     break
    else continue loop