IIS 7 Force Fresh Images

Question

How do I force IIS 7 to not cache images for a particular page?

Answer 1

I would have thought that it is your browser doing the caching.

In any case one way around this as long as your link is not statically declared in the html, is to append a random number on the end of the images url:

<img src="http://mywebsite/images/mypic.png?a=123456" />

the argument means nothing because you are doing nothing with it, but to the browser it looks like a new uncached link.

How you put that random number on the end is up to you:

<img src="javascript:getMyLink();" />

or from the code behind:

Image myImage = new Image();
myImage.Source = "myurl?a=" + Guid.NewGuid().ToString();
someOtherControl.Controls.Add(myImage);

(of course this is pseudo code, you need to check that the property names are correct).

Answer 2

In IIS7, you can do this either declaratively in your web.config, or programmatically.

<location path="YourPath">
  <system.webServer>
    <staticContent>
      <clientCache cacheControlMode="DisableCache" />
    </staticContent>
  </system.webServer>
</location>

The programmatic solution requires a simple HttpModule that's registered to run for all requests in Integrated mode, where you look for the URLs that you're concerned about. Then call:

context.Response.Cache.SetCacheability(HttpCacheability.NoCache);

FWIW, you may want to consider disabling client-side caching only, while enabling server-side caching, by using HttpCacheability.ServerAndNoCache. Also, if you add a query string on the image names, you will prevent server-side caching by http.sys.

In case it helps, I cover techniques like these in detail in my book: Ultra-Fast ASP.NET.