Sending Email with the logo / Attachment

I am trying to send my website logo with the Email. The logo should appear in the bottom of the message body. Though, I wrote the HTML in the message body, I am not able to show it in the email (Email is working, but no logo)
this is my code for message body:
String MessageBody = "Dear Dr. " + Lastname + "<br /> <br />" + "Thank you for registering " + "<br /> " +"<br /> " + "<b><u>Please save your username </u></b>" + "<br /> <br /> " + "Your UserName: " + UserName + "<br />" + "<font size=4><i> The web-platform will be launched shortly. You will receive an email notification from " + "<a href=\"webmaster@abcdef.ca\"> webmaster@abcdef.ca </a>" + ...