Upload as Teaser Background
Try to use Background Images Formatter module, hopefully it will fulfill your requirement.


  Background Images Formatter module provides an image formatter who allows you to set an image
  in background of a div. The images are from a field of an entity and
  not from a configuration page or sth else, so it's very easy to setup
  and manage.


Change selector value to whatever you want in manage display section (explained in attached screen shot)