Heather Perhaps you could check the Files API
Well, if everything would be that simple. File access is totally different permission to request from the users, and actually that is too much access for application like that. It also can be blocked by Google Play Store security review. And it is definitely much more complex to setup for users, which contradicts the idea of the applicaiton - just one button and you are done.
However, I think if the goal is just to filter our WhatsApp photos, we don’t need to overcomplicate things like that. I am sure there is a way to filter them out even with current access level. If that going to be common request, I think we can come up with some solution.