IIS 7.5 and images not being cached

Question

I cannot get the image files to cache. I have tried everything that I have found on this site and others and still cannot get them to cache.

Web config setting that I have tried

    <staticContent>     <clientCache cacheControlMode="UseMaxAge" cacheControlMaxAge="1.00:00:00" />     </staticContent>     <httpProtocol allowKeepAlive="true" />       <caching enabled="true" enableKernelCache="true">     <profiles>     <add extension=".png" policy="CacheUntilChange" />     <add extension=".jpg" policy="CacheForTimePeriod" duration="12:00:00" />     </profiles>     </caching>   

Here is the response headers for 1 of the images

    Key Value     Response    HTTP/1.1 200 OK     Cache-Control   no-cache     Content-Type    image/png     Last-Modified   Thu, 16 Dec 2004 18:33:28 GMT     Accept-Ranges   bytes     ETag    "a1ca4bc9de3c41:0"     Server  Microsoft-IIS/7.5     X-Powered-By    ASP.NET     Date    Fri, 18 May 2012 13:21:21 GMT     Content-Length  775 

Answer 1

The following should cause the browsers to cache your images:

<staticContent>     <clientCache cacheControlMode="UseMaxAge" cacheControlMaxAge="1.00:00:00" /> </staticContent> <httpProtocol>     <customHeaders>         <add name="Cache-Control" value="public" />     </customHeaders> </httpProtocol> 

The <caching>...</caching> block is for server-side caching, not client side caching.

Answer 2

In case anyone needs to configure your site as Chrome Audits or GTMetrix require I've configured my environments with the following (thanks to Marco's answer):

<clientCache cacheControlMode="UseMaxAge" cacheControlMaxAge="365.00:00:00" /> 

using 365 days and both tools took that value as acceptable for a cache time.