Hello, I am sharing my custom slim frame for lithophane photos. This one is created for lithophane size 240x160x4mm.
It will not work for scaling. Original file attached, ammend the size to fit yours picture accordingly. Hole for cable located at left bottom back side, dia 5mm.

Printing info:
I used PLA from Aurapol brand, Black.
Coolplate settings: BED 1st layer 45C, other layers 45C > that removed warping problems. AUX Fan = Off, Object Fan 70% ; 100s

PLA settings: 1st layear 230C, other layers 230C to keep print speed on normal (=100%)

Front and top glass closed.

Read more info here: Frame on referencial photo has trays on back face, I though I would need to place LED here, but at the end I end up only placing LED strips around the frame. Uploaded version of frame does not have trays for LED anymore, native file has them suppressed, be aware that they will not be ammended automaticaly as frame itself !

Purchased hardware:
LED link: https://eshop.ledsolution.cz/cob-led-pasek-8w-m-12v-bez-kryti-ip20/?variantId=119605
Trafo link: https://eshop.ledsolution.cz/led-zasuvkovy-zdroj-trafo-s-vypinacem-12v-24w/
+ DC connectors.

Link to Lithophane creator here: https://3dp.rocks/lithophane/ on Prusa site, you can follow up the tutorial for Lithophane if you like.
I prefer to print my lithophanes photos horizontally insetad of vertically, I like the cartoonish look, the artefacts are from 3m distance none-recognizable and the quality is perfect, print time is 4x faster then vertically.