Embed image in css for e-mail

[Bob Ross]

I am trying to make a function for my web site that will send an e-mail to new users. This email is going to be in HTMl format and I want to include images.
Now I can embed images using -

Dim box As New LinkedResource(HttpContext.Current.Server.MapPath( "~/Images/box.gif"), Net.Mime.MediaTypeNames.Image.Gif)
box.ContentId = "el_box"
htmlView.LinkedResources.Add(box)

and -

<img src="cid:el_box" ></img>

in the HTML. But what I would like to do is use an embedded image in the css i.e -

.bt {
height:15px;
margin:0 -6px;
background:url(cid:el_box) 100% 0 no-repeat;
}

I can use the same method for attaching the image to the email as above but this will then only display in outlook and not hotmail or googlemail.

Anyone know how to embed an image for use with css inside an email?

I am using vb.net version 2.

[Plater]

webmail programs might just blanket BLOCK that type of interaction with css/images/email?