验证码的生成

test.aspx
前台

                <asp:ImageButton ID="yzm" runat="server" ImageUrl="ShowExPwd.aspx" /> 
<asp:LinkButton ID="ChangeCode" runat="server" Text="看不清楚？换一个验证码" OnClick="ChangeCode_Click" /> 
<asp:Button ID="Button1" runat="server" OnClick="Button1_Click" Text="Button" />

        <asp:TextBox ID="a" runat="server"></asp:TextBox>  

test.aspx.cs

 protected void ChangeCode_Click(object sender, EventArgs e)
    {

    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        if (String.Compare(Request.Cookies["yzmcode"].Value, a.Text, true) != 0)
        {
            Response.Write("<script>alert('验证码错误!')</script>");
        }
        else
        { Response.Write("<script>alert('验证吗正确!!!')</script>"); }
    }

ShowExPWd.aspx.cs

 protected void Page_Load(object sender, EventArgs e)
    {
       //string sr = this.Request.QueryString["temp"].ToString();
      // this.Image1.ImageUrl = Server.MapPath("/images/1.bmp");
       this.CreateCheckCodeImage(RndNum());     

    }

        private string RndNum() 
        { 
            int number; 
            char code; 
            string checkCode = String.Empty; 

            System.Random random = new Random(); 

            for (int i = 0; i < 4; i++) 
            { 
            number = random.Next(); 
            if (number % 2 == 0) 
            code = (char)('0' + (char)(number % 10)); 
            else 
            code = (char)('A' + (char)(number % 26)); 
            checkCode += code.ToString(); 
            } 
            Response.Cookies.Add(new HttpCookie("yzmcode", checkCode)); 
            return checkCode; 
        }
    private void CreateCheckCodeImage(string checkCode)
    {
        if (checkCode == null || checkCode.Trim() == String.Empty)
            return;
        System.Drawing.Bitmap image = new System.Drawing.Bitmap((int)Math.Ceiling((checkCode.Length * 12.5)), 22);
        Graphics g = Graphics.FromImage(image);
        try
        {
            //生成随机生成器 
            Random random = new Random();
            //清空图片背景色 
            g.Clear(Color.White);
            //画图片的背景噪音线 
            for (int i = 0; i < 25; i++)
            {
                int x1 = random.Next(image.Width);
                int x2 = random.Next(image.Width);
                int y1 = random.Next(image.Height);
                int y2 = random.Next(image.Height);
                g.DrawLine(new Pen(Color.Silver), x1, y1, x2, y2);
            }

            Font font = new System.Drawing.Font("Arial", 12, (System.Drawing.FontStyle.Bold | System.Drawing.FontStyle.Italic));
            System.Drawing.Drawing2D.LinearGradientBrush brush = new System.Drawing.Drawing2D.LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height), Color.Blue, Color.DarkRed, 1.2f, true);
            g.DrawString(checkCode, font, brush, 2, 2);
            //画图片的前景噪音点 
            for (int i = 0; i < 100; i++)
            {
                int x = random.Next(image.Width);
                int y = random.Next(image.Height);
                image.SetPixel(x, y, Color.FromArgb(random.Next()));
            }
            //画图片的边框线 
            g.DrawRectangle(new Pen(Color.Silver), 0, 0, image.Width - 1, image.Height - 1);
            System.IO.MemoryStream ms = new System.IO.MemoryStream();
            image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
            Response.ClearContent();
            Response.ContentType = "image/Gif";
            Response.BinaryWrite(ms.ToArray());
        }
        finally
        {
            g.Dispose();
            image.Dispose();
        }
    }