I am trying to get Thumbnail to display in a table view. But am getting the Broken image symbol. See image below.
You should use a Picture library to store images and it has the functionality to load thumbnails.
Adding a Picture Content type to a document library don't create the thumbnails as expected. On the other hand in case of Picture Library it creates new thumbnail for each picture uploaded into a hidden folder
Details on enabling the same in a document library require extra effort as described in the article https://blogs.msdn.microsoft.com/syedi/2010/03/05/need-a-thumbnail-field-in-the-document-library-for-the-uploaded-picture-then-read-this-post/