Have you managed to find any tutorials on how to use those programs to make them?
I recall seeing an old (likely outdated, it was 10+ years ago made and didnt mention CNC) of them doing a “bas relief” where they could trace out a character/object from an image in GIMP or Photoshop, then use greys to make a “height map” then some how convert that into an STL file. Seemed like it was on the right track for what I wanted, but was missing a lot of information.