Hmm. Would it be possible to run these Apps in a VM like container? allow it access a dummy, empty folder to read from somewhat of a container for all apps? then there would be a manual transfer process between the shared folders after you've saved an image?
So when downloading an App it will ask would you want to run this in an isolated environment? and you can, so if it tries to scan over your photo gallery it will have an empty folder etc..
> to run these Apps in a VM like container?
That's what Xposed Framework does exactly.
> allow it access a dummy, empty folder to read from
That's what Xposed XPrivacyLua plugin does exactly.