title_body: Can I change the cover of a mobi/epub book? Can I change the cover of a mobi/epub book so that in Kindle or Aldiko reader software, the book cover is shown as my own customized cover?
upvoted_answer: Yes we can do that using opensource software like Calibre.
  
  
  Install the Calibre software and start the program.
  Copy the ebook.mobi file to your PC.
  Drag the book onto the Calibre software UI. It will get imported.
  Right click and select "edit metadata" for individual book you want to change.
  There is option to browse and select the cover that you want.
  Save the file. 
  Right click on the book and select open in directory, now copy the ebook.mobi file.
  Go to kindle directory on your device and delete the original ebook.mobi file and paste copied file in that location.
  
  
  The cover will be updated in your Kindle device. If its not updated try restarting the device. It will work after some time.
  
  The steps for epub files are similar, you will just need to copy the file to a different directory.
  
  (There are other programs like Cigil to edit epub files but Calibre can be used for both formats.)