文件（图片）强制下载

<a href="/student/stureg/downregcase" ><img src="http://images.cnblogs.com/reg/bmb.jpg" width="183" height="45"/></a>

//下载
function downregcaseAction(){
$file = "upload/regcase.jpg";
if(is_file($file)) {
header("Content-Type: application/force-download");
header("Content-Disposition: attachment; filename=".basename($file));
readfile($file);
exit;
}else{
echo "文件不存在！";
exit;
}

}