I have a server serving 12bit image and I can access the image through http, but since it is 12 bit image I am not able to load into System.Drawing.Bitmap(Stream stream).
Image format PNG bit depth 12
Image is here original 12 bit one
This is how the image should look once you are able to Load.
You may be able to read the image when using OpenCV library, since it also supports 12bit. You may also prefer to look for an adapter/wrapper, in order to use it in c#, since it is originally a C++ library
also look at those posts:
OpenCV: Working with 12bit gray scale raw data
What is the BMP format for Gray scale Images?
Convert 12-bit Bayer image to 8-bit RGB using OpenCV
hope it helps