Photo frame for vertical hanging

This is a photo frame designed so that a number can be connected together and hung vertically. One of the gallery photos shows our 9 grandchildren in one vertical display.
The part of this project that took longest was working out a convenient was to connect the photo frames together.
But first a little about the photo frame. I didn't want anything to do with glass. What does the glass do? Keep the photo clean - not worried about that, and always print another - and keep the photo flat. This