怎么把下面这段代码的验证码屏蔽或者改成固定的如1111，谢谢啦

后端：using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Data.SqlClient;

public partial class Login_aa : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{

}
protected void ImageButton1_Click(object sender, ImageClickEventArgs e)
{
    string email = Server.HtmlEncode(TextBox3.Text);
    string pwd = Server.HtmlEncode(TextBox4.Text);
    Model.user mod = new Model.user();
    mod.email = email;
    mod.pwd = pwd;

    BLL.user bll = new BLL.user();
    SqlDataReader  dr = bll.login(mod);

    if (CheckBox1.Checked)
    {
        SqlDataReader dr1 = bll.lo(mod);
        if (dr1.Read())
        {
            Session["_username"] = dr1["_username"].ToString();
            Session["_userid"]=dr1["_userid"].ToString();

            dr1.Close();
        }
        dr1.Close();
    }
    else
    {
        Session["_username"] = "";
    }

    if (Session["CheckCode"] != null)
    {

        if (TextBox1.Text.ToLower() == Session["CheckCode"].ToString().ToLower())
        {

            if (dr.Read())
            {
                Response.Redirect("ACIndex.aspx");



                Model.user mol = new Model.user();
                mol.userid = Convert.ToInt32(Session["_userid"]);

                BLL.user bllu = new BLL.user();
                int r = bllu.loginLastTime(mol);
                SqlDataReader dr2 = bll.lo(mod);
                if (dr2.Read())
                {
                    Session["_username"] = dr2["_username"].ToString();
                    Session["_userid"] = dr2["_userid"].ToString();
                    dr2.Close();
                }
                dr2.Close();
            }

            else
            {
                Common.MessageAlert.Alert(Page, "账号或密码错误，登入失败！");
            }

        }
        else
        {
            Common.MessageAlert.Alert(Page, "验证码错误！");

        }



    }

}
}

Email	/asp:TextBox
密码	/asp:TextBox
验证码	/asp:TextBox
	记住用户名