Hi Andreas, and thanks again.
Here's a quick follow-up on the --with-zlib=/usr/local thing.

--- In exiv2@..., "Andreas Huggel" <ahuggel@...> wrote:
> > the -L/usr/local/lib switch was required because otherwise libtool
> > wasn't able to find the libraries for libz (aka zlib): in
> > C:\msys\1.0\local\lib (mounted in /usr/local/lib) I have the following
> > files from the GnuWin32 package of zlib:
> > libz.a
> > libz.dll (renamed from the zlib1.dll)
> > libz.dll.a
>
> An additional option --with-zlib=/usr/local to configure should take
> care of this
>

Oddly enough it did not work out on my system. Here's the relevant
output from make:

../libtool --mode=link g++ -no-undefined -o libexiv2.la basicio.lo
bmpimage.lo canonmn.lo convert.lo cr2image.lo crwimage.lo datasets.lo
error.lo exif.lo futils.lo fujimn.lo gifimage.lo image.lo iptc.lo
jp2image.lo jpgimage.lo makernote.lo metadatum.lo minoltamn.lo
mrwimage.lo nikonmn.lo olympusmn.lo orfimage.lo panasonicmn.lo
pngimage.lo pngchunk.lo preview.lo properties.lo psdimage.lo
rafimage.lo sigmamn.lo pentaxmn.lo sonymn.lo tags.lo tgaimage.lo
tiffcomposite.lo tiffimage.lo tiffvisitor.lo types.lo value.lo
version.lo xmp.lo xmpsidecar.lo localtime.lo -rpath /usr/local/lib
-version-info 7:0:2 -lz -lm

*** Warning: linker path does not have real file for library -lz.
*** I have the capability to make that library automatically link in when
*** you link to this library. But I can only do this if you have a
*** shared version of the library, which you do not appear to have
*** because I did check the linker path looking for a file starting
*** with libz but no candidates were found. (...for file magic test)
*** The inter-library dependencies that have been dropped here will be
*** automatically added whenever a program is linked with this library
*** or is declared to -dlopen it.

*** Since this library must not contain undefined symbols,
*** because either the platform does not support them or
*** it was explicitly requested with -no-undefined,
*** libtool will only create a static version of it.
ar cru .libs/libexiv2.a basicio.o bmpimage.o canonmn.o convert.o
cr2image.o crwimage.o datasets.o error.o exif.o futils.o fujimn.o
gifimage.o image.o iptc.o jp2image.o jpgimage.o makernote.o
metadatum.o minoltamn.o mrwimage.o nikonmn.o olympusmn.o orfimage.o
panasonicmn.o pngimage.o pngchunk.o preview.o properties.o psdimage.o
rafimage.o sigmamn.o pentaxmn.o sonymn.o tags.o tgaimage.o
tiffcomposite.o tiffimage.o tiffvisitor.o types.o value.o version.o
xmp.o xmpsidecar.o localtime.o
ranlib .libs/libexiv2.a
creating libexiv2.la
(cd .libs && rm -f libexiv2.la && cp -p ../libexiv2.la libexiv2.la)

while appending an additional -L/usr/local/lib at the end of the
libtool invocation seems to do the trick.

I'm just leaving this here as a hint, I don't quite know what the best
course of action would