Add option to exclude page images in the Child theme builder

I built a new website for a photographer and I'm allowed to sell it as a child theme. The product I sell and the final version of the live website of the photographer will vary in small things. So I can't use the live website to show as a demo site.

Now I'm thinking about how I can solve this problem regarding the photographs. It's important that the original photographs are not part of the theme or download for my clients. But it would be great to show them on the demo site, because it would encourage more people to believe in this theme and buy it.

I don't want to go the way and built two demo sites (one for showing and one for download). That's to much duplicate content. So I wanted to ask if there's a possibility to show a demo site and get other photos into the child theme. Does that make sense? There should be different photos in the downloaded child theme than in the demo site. Is there any possibility to do this?