Lithophane frame for 200x150mm lithophane, you should be able to scale it up/down. I printed mine in wood filament and stained it.
Using light defuser is recommended if you don't want to see the LED strips. I used baking paper and folded it until i was satisfied with the results.
It can be placed on a shelf or you can mount it on a wall.

Print instructions

Printed mine in 0.2 mm layer height with woodfill and it looks awesome.
Use pegs
Depending on where you want to have your power source print the part with hole.
Tolerances for the back cover are designed to be fairly tight so when u paint it no glue should be necessary.
Easiest way to put it together is to glue the front of the frame and then connect the parts named: top/bot and sides. Then after gluing LEDs to the back close the back cover by connecting it to the rest.