public function thumbnail($fileName = null, $width = null, $height = null, $crop = null)
    {
        //Check if it's an alias as the only parameter after $filename
        if ($width && !$height && !$crop && $this->isAlias($width)) {
            return $this->getAliasedUri($fileName, $width);
        }

        $thumb = $this->getThumbnail($fileName, $width, $height, $crop);

        return $this->getThumbnailUri($thumb);
    }