I designed this box type display frame to display my child's pre-mounted art and crafts which are taller. It prints in 4 parts (print 2 each of the short and long sides) and assembles together easily. It fits artwork mounted on 8.5 Inch / 21.5 cm square backing boards which seems to be a standard size.
It features slots to cut and insert PlexiGlass cover to keep out dust - a 1mm or 2mm thickness plexiglass cover should fit nicely.
FreeCAD design files are provided if you want to make any edits
The author hasn't provided the model origin yet.