public function getAvatar()
    {
        $avatarUrl = null;
        $avatarWidth = 0;

        // find the biggest image
        if (!empty($this->response['pictures']['sizes']) && is_array($this->response['pictures']['sizes'])) {
            foreach ($this->response['pictures']['sizes'] as $picture) {
                if ($picture['width'] > $avatarWidth) {
                    $avatarUrl = $picture['link'];
                    $avatarWidth = $picture['width'];
                }
            }
        }

        return $avatarUrl;
    }