Item images appear in FireFox but not Internet Explorer 6

I'm having some problems with some JPEGs that I uploaded as items. The square thumbnails, regular thumbnails, and full-size images appear just fine in Firefox. In Internet Explorer 6, though, the images don't appear. I just get a box for the image with the red x inside.

I tried downloaded the JPEGs from Firefox, then viewing opening them locally in IE. They still don't show in IE.

I'm not having any problem, though, seeing thumbnails and full-size images in IE6 on other Omeka installs, e.g.,

Does anyone know what could be causing this problem?

Sorry for the amateur question. It turns out that the files were in CMYK, not RGB. I'm not sure why they came to me that way, but it was an easy fix.

Dude! Thanks for posting this info! We just had the same problem! Now solved in less than a minute thanks to you.