adding expires but not show up in headers

[angelochen960]

Hi,

I added a expires as follow:

location ~ ^/images/ {
        root /var/www
        expires max;
}

if I do a curl -I http://localhost/images/sample.jpg, I got following
headers, but can not find the "Expires" in the headers, what I did wrong
here? Thanks.

HTTP/1.1 200 OK
Server: nginx/1.4.1
Date: Wed, 19 Jun 2013 03:52:13 GMT
Content-Type: image/jpeg
Content-Length: 17584
Last-Modified: Wed, 19 Jun 2013 02:12:31 GMT
Connection: keep-alive
ETag: "51c1138f-44b0"
Accept-Ranges: bytes

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,240201,240201#msg-240201