Special Text Boxes Plug-in causing insecure elements

Back again.
I have a Plug-in installed on a website called Special Text Boxes that is serving up insecure images.

Is there something I can do to resolve this, or would I need to contact the Plug-in Developer?

The url is https://www.spottydog.com.au

Regards
Iain

https://wordpress.org/plugins/ssl-insecure-content-fixer/