a链接点击下载图片到本地（php）

$url="http://pan.baidu.com/share/qrcode?w=150&h=150&url=http://gandao.my".U('Question/index',array('id'=>$id));   //图片路径
$file_name = time().'.png';    //保存的图片名称
header('Content-Description: File Transfer');
header('Content-Type: application/octet-stream');
header('Content-Disposition: attachment; filename='.$file_name);  
header('Content-Transfer-Encoding: binary');
header('Expires: 0');
header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
header('Pragma: public');
header('Content-Length: ' . filesize($url));
ob_clean();
flush();
readfile($url);
exit;