version 3 of ps express app cannot save or open photos. The advice to go to Settings/Privacy/Photos and then give ps express permission is not possible since the app does not appear to have requested permission and is therefore not listed as an app to enable.
I am running version 3.0 on an iphone with iOS7. I just uninstalled and reinstalled the app to verify this. In settings>privacy>photos, PS Express is listed and has a blue icon. If it does not have the slider on the right side with a green background, then you need to slide it to the right to allow the app to access your photos.
I have ipad 2 and i have tried unistall reinstall and ps express is not listed in settings> privacy>photos so I cannnot give it permission to access photos. Guess I will have to get some other photo proceesing software.