download latest image files from server

We are opening image file(.jpeg,.png) in silverlight control embedded in child window created as below-

var StatusCardWindowNew = window.showModelessDialog(url, window, sFeatures); 

when this file is modified on server, this silverlight application is not downloading latest image file unless navigate to other URL or page refresh happens.

Any ideas on this?
Why IE (8 and above) is not downloading latest image files from server when these are modified there?

Thanks in advance..

Shwetank

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shwetank