I made this simple Shadow-Gap Frame model which can take 150x150mm (5,9x5,9 inch) paintings, photos or one of my Island models.

You can use double sided tape to fix your painting and hang it on your wall (use the through hole).

Scale it up or down if you have bigger or smaller paintings/models.

Dimensions are 180x180x18 (7.1x7.1x0.7 inch) @ 100% scale.

Here is the Hawaii Island Model that i used for my frame