Individual Background on a topic or a subtopic


Now, when I am slowly going through the creative process, there is another question. I created an overview slide.
and I want to fill in the slide of the stack topic
so I drill down, and there I see a blurred picture with parts of other pictures that were intended for other slides

Now, the question is – how can I change the slide background so that would show the full-size high-quality picture I keep in mind for this slide?