In the body of the email add an HTML image and simply set the URL as shown below.
1. Save the image base64 stirng in a variable.
string image = "data:image/png;base64," + Convert.ToBase64String(bytes);
2. Then add an HTML image in the body of the email.
msg.Body = "<img src = '" + image + "' />";
msg.IsBodyHtml = true;