Display thumbnail image with categories

Hi there,
I am hoping to use this plugin on my website and from your demo and showcase page it appears that categories can be displayed with an image. The website on your showcase is exactly how I want to set my page up. However I cannot see where to add a thumbnail or image to the Directory Categories.

http://www.sharedsorrows.com/business-directory/

Can you help please.

Kind Regards

https://wordpress.org/plugins/business-directory-plugin/