Convert byte array to Image in C# .Net

I have this in my Controller, and when recieve message the attachment don't have an extension and doesn't know how to open. What to do in this code: 

 public async Task<ActionResult> Contact(EmailFormModel model)
        {
            if (ModelState.IsValid)
            {
                var body = "<p>Email From: {0} ({1})</p><p>Message:</p><p>{2}</p>";
                var message = new MailMessage();
                message.To.Add(model.FromEmail);
                message.Subject = "Your email subject";
                message.Body = string.Format(body, model.FromName, model.FromEmail, model.Message);
                message.IsBodyHtml = true;
                string base64 = model.newImageData;
                byte[] imagebytes = Convert.FromBase64String(base64);
                message.Attachments.Add(new Attachment(new MemoryStream(imagebytes,0,imagebytes.Length), "Image1")); 
                using (var smtp = new SmtpClient())
                {
                    await smtp.SendMailAsync(message);
                    return RedirectToAction("Sent");
                }
            }
            return View(model);
        }