google charts api - Problem

Code:


header('Content-Type: image/png');
echo $this->chart->getChart();

------------------------------------
public function getChart(){
    return $this->_execute();
}

private function _execute() {
    $ch = curl_init('http://chart.apis.google.com/chart?chid='.md5(uniqid(rand(), true)).'&'.http_build_query($this->_post));
    curl_setopt($ch, CURLOPT_HEADER, 0);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
    curl_setopt($ch, CURLOPT_POST, count($this->_post));
    curl_setopt($ch, CURLOPT_POSTFIELDS, http_build_query($this->_post));
    $response = curl_exec($ch);


    $file = fopen('/path/to/test/graph.png', 'w+');

    fwrite($file, $response);

    fclose($file);

    return $response;
}

Code:


header('Content-Type: image/png');
echo $this->chart->getChart();

Code:
$response = ltrim($response);