I created a book layout for a customer of mine both for print and also fixed EPUB. I created the EPUB version from the print version, naturally. When my customer tried to upload the EPUB version to Ingram/Spark, he got the following error message: "(OPF-029): /323371.epub: The file "OEBPS/image/1.jpg" does not appeart to match the media type image/jpeg, as specified in the OPF file." Unfortunately, I have no idea what that means and the Igram/Spark "common errors" page did not address the issue. So I came here. Not sure if this is the right forum, but since I exported this from InDesign (newest version), I thought I'd at least check.
I also have a second problem. Upon exporting the file from InDesign, I get a multiple warnings, "TOC text anchor not found." This is strange because I double and triple-checked the Table of Contents dialog box and "Make text anchor in source paragraph" is clearly checked. What's even weirder is that the first few times I exported this file as a fixed EPUB, I did not get this error. It just started appearing, though I made no changes to the TOC.
I was able to isolate the problem to the cover image. When, during the export process, I had the cover image selected as "Rasterize First Image" it would end up creating the error. Once I changed the cover image option to "Choose Image" and selected a cover image, the problem didn't appear again. Hope that was helpful.