They're made using a box frame. This is deeper than a regular picture frame, so you can put 3D objects in it.
As you can see, scrabble-like tiles work very well! (They're not Scrabble tiles, mind you. That's a registered trademark, and I don't have the rights to use that...No indeed. These are wooden letter tiles. Arranged in a crossword formation)
This one used a birch coloured frame from The Range, it matched really nicely with the wooden tiles. And I've used an 8x8 backing sheet to set them off.
They also came in white!
