@Kesa
It depends on how recently IE cached the images. I believe the site sends headers to cache for 2 weeks typically.
I've contacted the admin because I suspect the problem is something that can't be fixed by playing with the site's local rewrite rules or directory permissions. None of them have changed anyway, so that would indicate that it's something in the apache configuration (which I've no access to) that's currently blocking images. It's not a problem with any of the images per se, I even added one to be absolutely sure.
One for the hosting provider to look at.