I know nothing of the Google Slides API, but I'm just curious...
Is there a way to create an immovable watermark or image applied to a slide or slides via the Google Slides API, where the user would not be able to remove it from the slide, even if a copy of the presentation was made for their own Google Drive?
Currently, if I allow someone to make a copy of a Google Slides presentation, and have uploaded an image as a background for the slide, anyone could simply remove the background and replace it with an image of their own, or just simply remove it.