Hello,
From what I know, Additional image layer is something you can apply on top of the main image as an overlay. For example, you can set your additional image layer to have the left or right most part of the titlebar have a different color or design than the main image layer. This image can have different margin than the main image layer. "Persona" is a good example of how additional image layer can be use.
Basj,
Stardock Community Assistant.
