public static function add_screenshot($hubcourseid, \stored_file $file, $screenshotnumber) {
        $curl = new \curl();
        $params = array();
        $params['filetype'] = self::HUB_SCREENSHOT_FILE_TYPE;
        $params['file'] = $file;
        $params['courseid'] = $hubcourseid;
        $params['filename'] = $file->get_filename();
        $params['screenshotnumber'] = $screenshotnumber;
        $params['token'] = registration::get_token(MUST_EXIST);
        $curl->post(HUB_MOODLEORGHUBURL . "/local/hub/webservice/upload.php", $params);
    }