public function thumb($width, $height=null, $imageObj = null, array $options = [])
    {
        // get current  object's image in case there is no specific image given
        if(!$imageObj) {
            $imageObj = $this;
        }
        $thumbDirectory =  $width.($height ? 'x'.$height : "");
        $thumbPath = $imageObj->fileDirectory.'/'.$thumbDirectory.'/'.$imageObj->filename;
        $thumbUrl = null;

        if(file_exists(base_path($thumbPath))) {
            $thumbUrl = asset($thumbPath);
        }else{
            if($this->createThumb($imageObj, $width, $height, $options)) {
                $thumbUrl = asset($thumbPath);
            }
        }

        return ($thumbUrl) ? $thumbUrl . "?" .strtotime($imageObj->updated_at) : null;
    }