From the readme
"If you want to keep the transparency of an uploaded image, you need to set the background color value to transparent."

This implies to me that you need to have a transparent background to start with.

Having used various photo tools to remove backgrounds and then clean up what is left manually.
I doubt there is a photo tool that can do this automagically and give a satisfactory result.

So I cannot see that IH would be set up or able to do this either.