How to attach a image on mail in HTML format

You have to make use of a combination of both Alternate Views and Linked resources in order to embed images in e-mail.

Imports System.Net.Mail
Imports System.Net.Mime

Public Class EmailMessage

Sub New(ByVal body As String, ByVal isHtml As Boolean, Optional ByVal subject As String = DefaultSubject)

        p_messagesubject = subject
        Message.Subject = MessageSubject
        Message.Priority = MailPriority.High
        Message.IsBodyHtml = isHtml

        If isHtml Then
            p_htmlmessagebody = body
            Dim htmlContent As ContentType
            htmlContent = New ContentType("text/html")
            Dim htmlView As AlternateView
            htmlView = AlternateView.CreateAlternateViewFromString(HtmlMessageBody, Nothing,
 MediaTypeNames.Text.Html)
            
            Dim logo As LinkedResource = New LinkedResource("c:\mylogo.jpg")
            logo.ContentId = "MyEmbeddedLogo"
            logo.TransferEncoding = System.Net.Mime.TransferEncoding.Base64

            htmlView.LinkedResources.Add(logo)
            Message.AlternateViews.Add(htmlView)
        Else
            p_messagebody = body
            Message.Body = MessageBody
        End If

    End Sub

End Class

Now, in order for the logo to show up you have to have a standard HTML img tag inside the HtmlMessageBody whose src attribute is set to the name of the ContentId

<img src="cid:MyEmbeddedLogo" />