I was recently gifted with a couple nice big pieces of 1/4" white acrylic (not Proofgrade but still very nice) and I decided to use it to experiment with doing a lithophane.
I chose this photo of a night-blooming cereus that I took of the one in my yard that bloomed last year:
I used the new portrait mode on an iPhone XS to isolate the flower from the background, and it worked great!
Here’s the resulting lithophane:
It’s a start!
The process I used was: photo --> .stl model --> depth map --> Photoshop convert to PNG --> Glowforge.
Edit: process description is now available here --> How I made my lithophane