public function setHeaderFields()
    {
        $cimageVersion = "CImage";
        if (defined("CIMAGE_USER_AGENT")) {
            $cimageVersion = CIMAGE_USER_AGENT;
        }
        
        $this->http->setHeader("User-Agent", "$cimageVersion (PHP/". phpversion() . " cURL)");
        $this->http->setHeader("Accept", "image/jpeg,image/png,image/gif");

        if ($this->useCache) {
            $this->http->setHeader("Cache-Control", "max-age=0");
        } else {
            $this->http->setHeader("Cache-Control", "no-cache");
            $this->http->setHeader("Pragma", "no-cache");
        }
    }