While i am aware of Free CNC and freely available softwares like bmp bender etc.
i studied research papers, regarding this topic.

With freely available techniques from the Internet it is not* guaranteed that
you get no extrusions at the models silhouette, the further the Z-axis goes.

* https://blender.stackexchange.com/questions/56172/bas-relief-model-from-a-3d-model-scene

Regards
Stefan

Maybe this can interest you, if you have photos of object wished ?
http://www.regard3d.org (free)
https://www.3dflow.net/3df-zephyr-free/

Personally I am for sharing information, but I think one is free to share, or not,said this, these bas-reliefs can also be done in other ways with Blender (https://blender.stackexchange.com/questions/1161/how-to-make-a-displacement-map-from-existing-3d-geometry), then use that image generated and with the Heightmap script you have a nurbs surface , using a displacement image.

an example made with a displacement map and heightmap script

Is that produced from an 8-bit or 16-bit image?

Is a simple jpg image.. ;)

one solution is here

https://youtu.be/ZXPn2PF_Wy4


http://3d-relief.blogspot.co.uk/2012/03/video-tutorials.html


I would assume you could create an image and use Rhino to apply the image as displacement- if you needed a nurbs surface. - not tested by me. I would just use the mesh

> one solution is here

i would say one solution was there.

Regards
Stefan