asp.net生成验证码

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.IO;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Drawing.Imaging;

namespace ASPNET.wzh.shopDoNet
{
    public partial class getCode : System.Web.UI.Page
    {
        private Bitmap validateimage;
        private Graphics g;
        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                string VNum = MakeValidateCode();
                Session["getCode"] = VNum;
                ValidateCode(VNum);
            }
        }

        public void ValidateCode(string VNum)
        {
            validateimage = new Bitmap(35, 12, PixelFormat.Format24bppRgb);
            g = Graphics.FromImage(validateimage);

            g.DrawString(VNum, new Font("宋体", 10), new SolidBrush(Color.White), new PointF(0, 0));
            g.FillRectangle(new LinearGradientBrush(new Point(0, 0), new Point(110, 20), Color.FromArgb(138, 238, 238, 255), Color.FromArgb(38, 238, 238, 255)), 0, 0, 120, 30);
            g.Save();
            MemoryStream ms = new MemoryStream();
            validateimage.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
            Response.ClearContent();
            Response.ContentType = "image/gif";
            Response.BinaryWrite(ms.ToArray());
            Response.End();
        }

        string MakeValidateCode()
        {
            char[] s = new char[] { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9' };
            string num = "";
            Random r = new Random();
            for (int i = 0; i < 4; i++)
            {
                num += s[r.Next(0, s.Length)].ToString();
            }
            return num;
        }
    }

}

另外在需要显示验证码的地方加入

<asp:Image ID="imgGetCode" runat="server" ImageUrl="getCode.aspx" />