Image not showing up in email template when using constant to pass that in template

Hi Experts,

I need your help in resolving my issue.

I have one HTML template which is being attached in send email node in a process model. I want to add one image in that template. But up on adding the image via a document constant that we are passing in a template

  its not showing up like this in the email that we are getting: 

But when we are using URL for adding an image in the template its working fine.

My question is how to add an image in an HTML template that it will display in the email but using Image file document constant in Appian?