Simple System Images

Once activated go to 'Media' and select 'List View' screenshot-1.png

Just select the image(s) you want to make System Images and use the Bulk actions drop down to Mark or Unmark system images screenshot-2.png

You can see if an image is a system image in list view screenshot-3.png

You can also see if an image is a system image when viewing the image directly screenshot-4.png