First, a comment on the code. Using a plus sign to concatenate text is unreliable and not generally practiced. You should use the ampersand to concatenate text (&). What follows is what I know from reading; confess I've never had to worry about non-native users seeing images beyond what I've manually inserted into an email.
It is possible to embed the image in the message by first attaching it so that the html can add it "in line" using the cid: tag. However, the results will not be the same for everyone - depending on what mail client they're using. Here's a decent article on that subject, wherein I'd say the best solution may be to place the image in a public drop box.
Your image tag would look like <img src='cid:MyLogo.jpg'" & "width='600' height='45'>
I suppose another approach would be to use an email template that you have manually embedded the image into.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.