While working on a magento e-commerce website i found that customers were receiving the “unsecure items” warning during the checkout process.  I used various tools to find the offending item, but was unsuccesful, nothing would tell me what this “unsecure item” was. One thing that i had ignored but suspected was a reference in Firefox’s “View Page Info” window under the media tab.  The address column identified it as “data:image/gif,AAAA” and the size was “unknown” and the type was “image.”  I investigated this item further and found a reference to it inside the lightbox CSS file used as a background-image to create some workaround for an IE issue with the lightbox.  I replaced the base64 background-image reference with a spacer GIF file url, updated the magento cache and voilà, no more unsecure item warnings in IE!