I presume from the way you describe it that it needs to be a dynamic image as opposed to a static filler. Your best bet is use of custom sendemail or a scripted alert action (Upon detection of defined pattern, the script is triggered which then does the e-mail composition for you.
Here are some links that will help (though old are still relevant in parts)
I have a one static image that needs to be send to the user, no dynamic images. Is it possible that I keep the image in some location and using sendemail + html combination to load the image in the body and send it ? Please advise ?