Tony,
This may have broken with the latest release. I have duplicate logos on my invoices and the Image column is there, but the image is not. The Image is showing up on the "Thank your for your order" screen after checkout.
I am working on something unique with Olesya that modifies the Invoice Email. You may want to chat with her.
Packed Mod:
https://www.dropbox.com/s/6pih1imkjzinhog/FasterThanYours-ImagesOnInvoice-v5_2_0.tar?dl=0
Image of the Invoice in Email
http://i21.photobucket.com/albums/b298/fasterthanyours/Images%20On%20Invoice%2003%20-%20Double%20Logos%20a...20pictures.jpg