How to use expert class settings for display suite for images? I've tried different combinations, but it's now working or showing up in chrome inspector...

I'm also using Bootstrap template, could that by a problem?

Or maybe I'm not filling out the information correctly in the field boxes?
Have you tried  Image Class.


  Extends the Image formatter by adding an option to add an element
  class.


It does not work in combination with Display Suite unfortunately as per this post: Merge Image Class into Display Suite