public function isImage( $exif=null )
    {
        $_ext   = empty($exif) ? self::$img_extensions : self::$exif_extensions;
        $tbl    = explode('.', $this->filename);
        $last   = end($tbl);
        return (bool) ($this->pathExists() && $this->exists() && in_array(strtolower($last), $_ext));
    }