title_body: Is there a way to make third party book (non-amazon) covers appear as screensavers on Kindle? So recently Amazon has introduced this feature which shows the cover of what you are currently reading on the lock screen of your Kindle reader (at least for Kindle Paperwhite 4 as far as I know).
  As I have both Amazon and third party books on my Kindle Paperwhite, I have noticed that this new feature only works for Amazon books. Meaning, when I am reading some third party book and lock the screen, I do not see it's cover (some generic Kindle screensaver pops-up instead).
  Has anyone else had this experience and are you aware of any practical ways to solve this?
  P.s. two additional points worth mentioning:
  
  I have reviewed the metadata of these third party books via Calibre and as far as I can tell, covers are present and are clearly identified as such within the metadata code;
  These third party books are recognised as “Personal documents” by Kindle (as opposed to Amazon books, which are properly recognised as “Books”).
upvoted_answer: After running some experiments I have finally managed to solve this issue for my Paperwhite4.
  For anyone having the same issue - follow this sequence:
  
  Take a side loaded document of any format
  Open it w Calibre
  Right click on it and press “Edit metadata”
  In a new window press the button “Download metadata” (it’s at the bottom of the screen)
  Follow thru with a dialog window
  Choose one of the book covers proposed by Calibre (do this step even in case you think your document already has a cover)
  Finish by pressing “Ok”
  Convert your document to mobi
  Hook up your kindle via USB
  Right click on the document in Calibre and choose “Send to device”
  Choose “Send specific format to”
  Choose “Main memory”
  Select mobi file from the list
  
  You are done. Your document’s cover will  display on the lock-screen.
  Essentially it appears that three things were key:
  
  downloading/ updating the file’s metadata and the cover via Calibre
  converting the file to mobi
  sending the file to kindle via USB (through Calibre as opposed to simple drag and drop using windows explorer)