And you can add a transparent background to you png image by change the 
<?php
    if ($ignore_transparent == 0) {
        imagefill($destimg, 0, 0, imagecolorallocatealpha($destimg, 255,255, 255, 127));
        imagesavealpha($destimg, true);
    }
?>
to
<?php
    if ($ignore_transparent == 0) {
        $temp = imagecolorallocatealpha($destimg, 255,255, 255, 127);
        imagefill($destimg, 0, 0, $temp);
        //if set the default color or white or magic pink then use transparent color
        if ( ($bgcolor == 0) || ($bgcolor == 16777215) || ($bgcolor == 16711935) )  {
            $bgcolor = $temp;
        }
        imagesavealpha($destimg, true);
    }
?>