Panel and Image resize issue

Hi all,
 
I have a simple webpage with radio buttons that makes panels visible or invisible.  There is no fancy thing going on in here.  The issue I am running into is that sometimes when i open the webpage (in IE or firefox) the image is scaled from original size to a very small thumbnail size.  If I refresh or right click on the image and select properties, the image goes back to the normal size.  This is really annoying.  Is this happening because of the images inside the panel or because of seomthing else.
 
Thanks in advance.
SK 
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