I don't think you need CDO to embed an image in an html body. CDO is useful because you can bypass the email app and work with the email server directly. The only reason I ever used it was to get around the security prompt we used to get at that time. It also allowed me to send mail without using my own email account.
I believe the tag you need is like "<img src=cid:ImageFileNameHere></img>"
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.