do.php:
if($_GET[‘ac‘]==‘dw‘) {
$file = ‘./12.jpg‘; //文件路径
$filename = basename($file); //要下载文件的名字
header("Content-Type: application/force-download");
header("Content-Disposition: attachment; filename=".($filename));
readfile($file);}
原文：http://blog.51cto.com/12363916/2088854