hi,
I've researched a bit more and now we've found out that it isn't about the http headers (headers of both a filtered and an unfiltered image are the same) but it's about internet explorers caching!
For some reason Internet Explorer doesn't cache the jpg that has the xml removed, and that's why it requests the image again when reloading the page. I'll do some experiments with other images that are filtered.
@keesj: Did you come up with the IEFilter yourself or is it based on documentation by someone else? Maybe there's a small modification possible that can convince IE to cache the image...
Simon
