Sure, but if I've deleted cover.jpg doesn't that trigger "No cover" or is it "No cover tucked away inside the ePub"?
On another note, but triggered by me playing with this plugin - I used Quality check to check for weird covers - it found some with multiples - I edited them with Sigil just deleting the Jacket files. I then redid Calibre's ePub to ePub conversion..... and the Jacket files reappeared??? It was like I had ticked the "Insert metadata" option - but I hadn't :-(
Any suggestions or should I repost as a Calibre problem??