Knack to webmerge and adding a png image

I am trying to get a png image sent to my webmerge pdf

So far i can easily get text fields, email addresses, and checkboxes sent over.

How can i get it to send a png image?

I followed this guide here: Dynamic PDFs and Documents with WebMerge - Knack Blog

It works for me perfectly, just need help sending the image.

Thank you!