Originally Posted by Sabardeyn
I know you can do a search with cover:true and determine which books have a separate cover file; cover:false for books without. You could use the last search to find the books that still need a separate cover.
After that I think you're stuck looking through the books.
cover:true only looks at Calibre (book details) to see if CALIBRE has a cover.
The Quality check Plugin can look INTO a book and test ('declared?' or first image?) covers (3 choices of check)