Yes, most client apps will work offline as they usually consist of basic gallery, button and text sections that do not need an internet connection to work.
Once your clients have installed their app on their mobile device and viewed all the images they will be able to view their album images again, even if they are not connected to the internet.
However, many of the more advanced features of MyPhotoApp that you may include in your marketing and business apps do require an active internet connection for the app to load.
These include: HTML sections, PDF sections, content section, Tracking section and dynamic gallery and text sections.