web.config expire header does not work for png files

Question

I am using this code in my web.config file at the root of my website to set an expiration header for my static content:

<staticContent>
    <clientCache httpExpires="Sun, 29 Mar 2020 00:00:00 GMT" cacheControlMode="UseExpires" />
</staticContent>

It seems to work fine for my css and javascript as Yslow does not give me an error for those anymore. However, it does show that all my png images on the page have no expiration header for some reason.

(2015/8/20) http://fonts.googleapis.com/css?...
(2015/8/20) http://www.google-analytics.com/analytics.js
(no expires) http://snippetspace.com/img/snippetspacelogo.png
(no expires) http://snippetspace.com/favicon.png
(no expires) http://snippetspace.com/img/iwebkitsliderimage.png

I am using Microsoft Azure websites, so only have access to the web.config file. Any ideas on how to configure this so that it also covers my png's?

Answer 1

Try adding the .png mime type explicitly:

<mimeMap fileExtension=".png" mimeType="image/png" />

Maybe remove before adding:

<remove fileExtension=".png" />
<mimeMap fileExtension=".png" mimeType="image/png" />