Some customers could have their screen rotation locked, due to their device settings. If they turn their device to landscape view and customer's picture does not change/rotate, be sure you ask them to unlock their rotation. They can change it through the Settings option on their device.
On Android, go to your home screen, open device settings, scroll to display, check/uncheck auto-rotate screen. Then just go back to the app.
They may also slide down from the top of their phone and their Shortcuts will appear. Ask them to scroll with their finger until they find Screen rotation settings. Check/uncheck auto-rotate screen.