Why your EPUB cover gets rejected

A cover issue is one of the most common reasons an EPUB bounces back from a publishing platform — and it's rarely about the image looking wrong. It's almost always about how the cover is declared inside the file, which a reading app or a human reviewer checks before it ever renders the image.

The cover has to be declared, not just present

Having an image file named cover.jpg somewhere in the EPUB isn't enough. The package file (the OPF) needs a manifest entry for that image explicitly marked with the cover-image property (EPUB3) or referenced via a meta name="cover" tag (EPUB2). Without that explicit declaration, reading systems and validators have no reliable way to know which image is the cover — even if it's the only image in the file.

Common ways this breaks

The cover image file exists in the archive but was never added to the manifest.
The manifest entry exists but the property/meta declaration marking it as the cover is missing or misspelled.
The declared cover file path doesn't match where the image actually sits in the archive (a broken manifest reference) — often from exporting or repackaging the EPUB after the cover was originally set.
The image itself is oversized (multi-megabyte, print-resolution files are common when reusing a print cover) — not always an outright rejection, but a frequent cause of slow processing or a size-based warning.

How to catch it before you submit

Run the file through the EPUB format checker above — it flags a missing cover declaration, broken manifest references, and images over 5MB as part of its structural check. Fixing the declaration itself (adding the right manifest entry or property) generally needs to happen in whatever tool generated the EPUB, since this checker reports the problem but doesn't rewrite your file's structure for you.

Ready to check your file? Upload it to the EPUB format checker.