. configure.ac needs changes to revert IMAGEMAGICK_LIBS to empty
value, because otherwise src/Makefile will cause Emacs binary to be
linked against the ImageMagick libraries, and the resulting binary
will then refuse to start if the corresponding DLL is not available
at run time. You can see the example of how we do that with
librsvg.

I'm not good at GNU Autotools stuff, sorry. Could you elaborate on this? I don't see that "IMAGEMAGICK_LIBS" would be assigned any value in "configure.ac". Nevertheless, on the linking stage I see:

-lMagickWand-6.Q16HDRI -lMagickCore-6.Q16HDRI

Is this what you meant? Can I just safely assign it to empty value then?

. dynamic-library-alist in w32-win.el should acquire an element
required for Emacs to know which DLL(s) to look for when
ImageMagick support is first required.

I assume adding something like:

'(imagemagick "libMagick++-6.Q16HDRI-5")

Is this correct?

. If there are several ImageMagick versions out there whose DLLs are
not binary compatible, you will need to add version checking, both
on init_imagemagick_functions and in dynamic-library-alist,
similarly to what we already do with some other image libraries,
like libgif, libjpeg, etc.

Well, I have no idea about that yet. I'm not a huge expert with ImageMagick. Perhaps somebody could clarify on that.