$ php -v 
PHP 5.3.3 (cli) (built: Dec 11 2013 03:29:57)
Copyright (c) 1997-2010 The PHP Group 
Zend Engine v2.3.0, Copyright (c) 1998-2010 Zend Technologies

$ git diff
diff --git a/data/module/gdthumb.php b/data/module/gdthumb.php
index 5d6afc8..2ab7d46 100644
--- a/data/module/gdthumb.php
+++ b/data/module/gdthumb.php
@@ -231,7 +232,8 @@ class gdthumb {

         $src_im = imageCreateFromPNG($path);

-      $colortransparent = imagecolortransparent($src_im);
+      $black = imagecolorallocatealpha($src_im, 0, 0, 0, 127);
+      $colortransparent = imagecolortransparent($src_im, $black);
       if ($colortransparent > -1) {
         $dst_im = $imagecreate($re_size[0], $re_size[1]);
         imagepalettecopy($dst_im, $src_im);