As far as I can gather there has to be an image, or the email in HTML, (I am guessing if the email is text only then placing an image would require it to be sent in HTML anyway) for the tracking to be successful, and again, link tracking is also tracked i.e. you get a report if a link within your email is clicked. The main track will also tell you how many times the email has been opened.
Good to hear MSGTAG is back, I will see if I can log on; if I go back I will keep Contact monkey ready in the background.