this do what you want:

use Tcl::Tk;
my $int = new Tcl::Tk;
$int->packageRequire('img::png');
open my $fh, "valid-xhtml10.png";
binmode $fh;
$int->mainwindow->Label(-image => $int->imageCreate('photo',
   -data=>join'', <$fh>,
   ))->pack;
$int->MainLoop;
[download]

your Tcl/Tk code probably misses 'binmode'
yet img::png...

as for related mailing list, you'll more chance on help on it because it is more on-topic.

PM is good resource but your question will not always find a person who could answer.