title_body: How do I have Calibre automatically create a cover image from a non-ebook file? I am an RPG publisher and use Calibre to maintain my research library (PDF, mostly) and my stock art library (various image files).
  
  When I load a PDF, Calibre automatically creates a cover image using the first page of the PDF.
  
  When I load image files, it cannot. I must assign the cover image explicitly. Is there a way to have Calibre automatically create a cover image from a 'book' that is a raster image (JPG or PNG format)?
upvoted_answer: I'm afraid this isn't the answer you need, and it's been a long time coming. Although I don't recall the method, be it via an add-on or whatever, I succeeded in using a jpg image of my own design (CS6) as a cover. It was available in the Calibre cover customization window, so applying title/author text in the usual way was no problem. So, yes, there's an easy to use method, and if I re-discover it before you do, I'll post the details.