--- t/png.t.orig	2011-04-28 16:53:40.149925007 +0800
+++ t/png.t	2011-04-28 16:55:24.229044665 +0800
@@ -19,13 +19,21 @@
 use strict;
 my $code = new Barcode::Code128;
 my $file = "t/code128.png";
-my $good;
-{
-    open IM, $file or die "Can't read $file: $!";
-    binmode IM;
-    read IM, $good, -s $file;
-    close IM;
-}
+my $expected_image = GD::Image->new($file);
+
 my $test = $code->png("CODE 128");
-print "not " unless $test eq $good;
+my $got_image = GD::Image->new($test);
+
+my $cmp = $expected_image->compare($got_image);
+print "not " if $cmp != 0;
 print "ok 2\n";
+
+if ($cmp & &GD::GD_CMP_IMAGE) { warn "The two images look different\n" }
+if ($cmp & &GD::GD_CMP_NUM_COLORS) { warn "The two images have different numbers of colors\n"}
+if ($cmp & &GD::GD_CMP_COLOR) { warn "The two images' palettes differ\n"}
+if ($cmp & &GD::GD_CMP_SIZE_X) { warn "The two images differ in the horizontal dimension\n"}
+if ($cmp & &GD::GD_CMP_SIZE_Y) { warn "The two images differ in the vertical dimension\n"}
+if ($cmp & &GD::GD_CMP_TRANSPARENT) { warn "The two images have different transparency\n"}
+if ($cmp & &GD::GD_CMP_BACKGROUND) { warn "The two images have different background colors\n"}
+if ($cmp & &GD::GD_CMP_INTERLACE) { warn "The two images differ in their interlace\n"}
+if ($cmp & &GD::GD_CMP_TRUECOLOR) { warn "The two images are not both true color\n"}