Hi Dan,
In theory, you could include it directly in the page of the email using HTML (with an expression with escape no):
<img alt="" src="data:image/png;base64,...
But in the past, most email clients didn't had support for it. I don't know if they are better now.
As an alternative, you could save the image to database, using the conversion function to change it to binary and than simply use a image widget.
If the image is "static", will not change, you can include as resource or deploy to target directory.
Hope this helps,
Cheers
Eduardo Jauch