I designed this Lithophane Lightbox for my sisters 30th Birthday but this can be used for any occasion. I've included the 30th Birthday top pane STL but also included a blank pane incase you don't want to put a Lithophane at the top of the box.
I've designed the box to fit 100x100mm Lithophanes which can be generated form: http://3dp.rocks/lithophane/ I'd suggest setting the Image settings to Positive Image and printing the Lithophanes standing on their edge with with a brim. I know this sounds pretty crazy as they are only 3mm thick so there's a risk of them falling, but as long as your bed is levelled correctly and your printer is calibrated well you it will work fine and yeild a much better quality print.
You can used pretty much any light coloured PLA filament (not transparent) for the Lithophanes. I've only tested white so far and it's worked out very well.
Note my Cura settings for the Lithophanes is 0.1 Layer Height, 100% Infill and 10mm Brim Width.
I haven't printed the box out yet as I'm still waiting for the last Lithophane to print out so note that this is a work in progress at this point and there may be minor issues I haven't been able to test yet.
My plan is to print this in Wood PLA and possibly stain to make it more authentic looking. I'll update with photos once I've completed the box.
0.1 for Lithophanes / 0.2 for the frame
Amolen Wood PLA
100% for Lithophanes / 10% for the frame