Here is a build album showing how I made this: https://imgur.com/a/gVwjZL2
Edit- Thanks everyone for the love, sorry I haven't been able to reply to all of the comments! I'll just make a mini-FAQ here to answer some of the questions I've been getting.
I originally considered firing up an Etsy shop to sell these when I started the project, but after making this one it is simply not feasible to make larger quantities of these the way I did it. The total printing time is about 5 days and I have to do a fair amount of post-processing on the lithophane to clean up imperfections. Someday I might buy a different type of printer that could do these much faster and higher quality, but the type I have in mind costs at least $2,000.
Since I might be selling these in the future, I don't want to release the print files freely. However, here are the things I used if you want to make one of these yourself:
https://www.lithophanemaker.com/Framed%20Lithophane.html
https://evergraphs.com/lithophane-light-panels/
https://www.amazon.com/gp/product/B01CCIKB5Q/ref=ppx_yo_dt_b_asin_title_o06_s00?ie=UTF8&psc=1
https://www.amazon.com/gp/product/B07KZQGWNN/ref=ppx_yo_dt_b_asin_title_o09_s01?ie=UTF8&psc=1
https://www.amazon.com/gp/product/B07CNQC695/ref=ppx_yo_dt_b_asin_title_o09_s00?ie=UTF8&psc=1