My son has taken up painting and some of his work is on cardboard carried canvas, which has no hook or frame to make a hook on. This frame (or the original) is able to hold it and hang on the wall.
The author remixed this model.
I complete re-implemented https://www.printables.com/model/195386-customizable-picture-frame in openscad, because it didn't work for me originally. I didn't reuse any code. I used the children feature of openscad.