I've come across an issue where some images on a site load under https but do not load under http.
For example if you go to https://www.mydomain.com/myimage.gif, the image appears fine, but if you go to http://www.mydomain.com/myimage.gif the image comes back with a not found error. This happens to only certain images. Other images load fine either way. Even images in the same directory as the problem images load fine.
I know that if SSL is not set up correctly I've seen a similar issue, but it's always been with the entire site, not with a few images.
This is on an IIS6 server.