Android should add the option for temporary data access. I would prefer turning on the access temporarily to send 1 photo, then turning it off a few minutes later.
https://developer.android.com/training/articles/security-tip...
See: https://developer.android.com/reference/android/Manifest.per...
If you don't mind sharing, what app are you referring to?
The file system itself should be well protected (on a non-rooted phone) as to prevent any unauthorized access to important data. Any app can only do whatever on the SD card if you give it permission to do so, but on the OS file system itself there isn't much they can do (again, on a non-rooted phone).
https://developer.android.com/training/secure-file-sharing/r...