public function mkThumbnail($src, $width = null, $height = null, $filename = null) {  
        if (!isset($width) && !isset($height))  
            return false;  
        if (isset($width) && $width <= 0)  
            return false;  
        if (isset($height) && $height <= 0)  
            return false;  
      
        $size = getimagesize($src);  
        if (!$size)  
            return false;  
      
        list($src_w, $src_h, $src_type) = $size;  
        $src_mime = $size[‘mime‘];  
        switch($src_type) {  
            case 1 :  
                $img_type = ‘gif‘;  
                break;  
            case 2 :  
                $img_type = ‘jpeg‘;  
                break;  
            case 3 :  
                $img_type = ‘png‘;  
                break;  
            case 15 :  
                $img_type = ‘wbmp‘;  
                break;  
            default :  
                return false;  
        }  
      
        if (!isset($width))  
            $width = $src_w * ($height / $src_h);  
        if (!isset($height))  
            $height = $src_h * ($width / $src_w);  
      
        $imagecreatefunc = ‘imagecreatefrom‘ . $img_type;  
        $src_img = $imagecreatefunc($src);  
        $dest_img = imagecreatetruecolor($width, $height);  
        imagecopyresampled($dest_img, $src_img, 0, 0, 0, 0, $width, $height, $src_w, $src_h);  
      
        $imagefunc = ‘image‘ . $img_type;  
        if ($filename) {  
            $imagefunc($dest_img, $filename);  
        } else {  
            header(‘Content-Type: ‘ . $src_mime);  
            $imagefunc($dest_img);  
        }  
        imagedestroy($src_img);  
        imagedestroy($dest_img);  
        return true;  
    }