...
use_ok('Tk::PNG');

my $file = (@ARGV) ? shift : "$FindBin::RealBin/../pngtest.png";

my $mw = MainWindow->new;
$mw->geometry('+10+10');
$mw->update;			#### Added by --cmv
sleep 10;

{
print STDERR "Photo 1\n";	#### Added by --cmv
    my $image = $mw->Photo('-format' => "png", -file => $file);
print STDERR "Photo 2\n";	#### Added by --cmv
    ok($image, "Loaded PNG image from $file");
print STDERR "Photo 3\n";	#### Added by --cmv
    $mw->Label(-image => $image)->pack;
print STDERR "Photo 4\n";	#### Added by --cmv
    $mw->update;
print STDERR "Photo 5\n";	#### Added by --cmv
}
...