On Fri, Mar 2, 2018 at 2:05 PM, Eli Zaretskii <eliz@gnu.org> wrote:

> >  Are there any other versions of libpng16-16.dll on that system?
> >
> > I ran the following:
> > $ find.exe / -name libpng16-16.dll
> > /cygdrive/c/Portable Programs/emacs-26.0.91-x86_64/bin/libpng16-16.dll
> > /cygdrive/c/Portable Programs/inkscape/libpng16-16.dll
> > /cygdrive/c/Program Files/emacs-25.1-x86_64-w64-
> mingw32/bin/libpng16-16.dll
> >
> > I found the old C:\Program Files\emacs-25.1-x86_64-w64-mingw32\bin on
> my path, removed it and restarted
> > Emacs, verified that it was not listed in (getenv "PATH"), but no luck.
> I still cannot display PNG images.
> >
> >  Does pngfix.exe work (it should be in the same directory as
> >  libpng16-16.dll)?
> >
> > Yes it does.
> >
> > $ ./pngfix ../lib/python2.7/idlelib/Icons/idle_16.png
> > IDAT OK  maximum 12 12 1070 2064 ../lib/python2.7/idlelib/
> Icons/idle_16.png
> >
> >  And finally, what is the value of libpng-version in your Emacs?
> >
> > libpng-version
> > 10634
>
> Strange.  I can only suggest stepping with a debugger through
> init_png_functions, to see what exactly fails there and why.
>

I did a binary search of my config and found the culprit. Sorry for the
noise!

I had the following hidden away in one of the gazillion config files:

(add-to-list 'dynamic-library-alist '(png "libpng15-15.dll"))

Removing this file fixed PNG support for Emacs 26.

Again, I'm very sorry I didn't think of this any sooner.
Alex