If i understand you correctly you just want to check how many times the image has been viewed? If so, then maybe the following...
If the image is stored on disk somewhere via an obscure URL, you can reference the image from the Email absolutely and then use a stats package (generally free from most hosts) to see how many times it has been accessed.
Obviously you will have to compete with mail clients blocking images from being downloaded.
I may have totally misunderstood your requirements though.