protected void Page_Load(object sender, EventArgs e)
{
  // Заполнение данных
  // ...
  
  if (!IsPostBack)
  {         
     // Import User Avatar
     imgPhoto.Src = Utils.Converter.GetImageUri(COLH.ConfigurableUser.Avatar);

     // ...
   }
}

<img id="imgPhoto" runat="server" src="~/Images/icon_user.png" height="150" width="150" />

<input type="file" id="openFileDialog" name="openFile" title="browse file" onchange="loadImage(event)"/>

             function loadImage(event)
             {
                 var file = event.target.files[0];
                 var reader = new FileReader();
                 var imgCtrl = document.getElementById("imgPhoto");

                 imgCtrl.title = file.name;

                 reader.onload = function (event)
                 {
                     imgCtrl.src = event.target.result;  
                 }

                 reader.readAsDataURL(file);
             }

<asp:LinkButton ID="lnkApply" 
        onclick="lnkApply_Click" runat="server"
        Font-Names="Cambria" Font-Size="Medium" ForeColor="#0099FF">Принять изменения
</asp:LinkButton>

        protected void lnkApply_Click(object sender, EventArgs e)
        {
            // Проверки...

            Model.User newAccount = new Model.User((int)Role);

            newAccount.Mail = Mail;
            newAccount.Post = Post;
            newAccount.Phone = Phone;
            newAccount.Login = Login;
            newAccount.Name = UserName;
            newAccount.AdditionalInfo = Description;
            newAccount.HashOfPassword = Controller.Secure.Hash(PasswordNew);
            newAccount.Specializations = spList;
           
            newAccount.Avatar = Utils.Converter.GetImageFromHTMLImg(imgPhoto);

            if (newAccount.RegisterNew() == DATA_MANAGE_DB_CMD_STATUS.SUCCESS)
            {
                 // Do smth.
                 
                 // go...
                 Server.Transfer("~/View/wfrm_accounts.aspx", true);
            }
            else
                 ShowMessage(COLH.CurrentMessage.Text);
        }

enctype="multipart/form-data"