I've moved your posting to the InDesign EPUB forum.
I'm pretty sure that you need text in your TOC, and not images. There may be a way of tricking it by "hiding" the text, but I've never heard of anyone doing it.
Steve, thanks so much for moving and answering.
Noted about trying to hide the text. I already made an attempt and I'm sorry to say it didn't work, at least not the way I did it.
If I were to make each chapter its own file, would the TOC generate from the names of each file? Then I might be able to build the TOC *and* keep my image headers.
Have you tried just putting in placeholder text and then deleting it for each chapter after? I know it would be a pain but EPUBs usually need little tweaks after they're exported to really work properly.