If a new browser session is opened then IE first reads all images also when IE cache settings are set to "Automatically".To allow access to cached files also in this case you can confiure your web server.
IIS
You have to add a new http header like this:
The number behind max-age is the age of the image
Apache
Please add those settings to httpd.conf:# enable expirationsExpiresActive On# expire GIF images in the client's cacheExpiresByType image/gif A86400ExpiresByType image/png A86400ExpiresByType application/x-javascript A86400