Multi-Item Drag Images
A multi-item drag image is displayed when the user drags multiple documents or items from one location to another. By default, the system displays a generic multi-item drag image, but you should replace it with a custom image that suits your app's design aesthetic.
Design a content-rich image. Ideally, the image should show a stacked representation of the actual content being dragged. For related guidance, see Drag and Drop.