验证码

login.aspx文件

<asp:TextBox ID="txtCode" runat="server"  HintTitle="请输入验证码" ></asp:TextBox>
<img src="valicode.aspx" onclick="javascript:window.location.reload();" />(刷新页面)
或
<span id="update" onclick="javascript:code.src='valicode.aspx?tm='+Math.random()" title="点击刷新验证码"><img src="valicode.aspx" id="code"/></span>(只刷新验证码)

login.aspx.cs文件

if (Request.Cookies["ValidateCookie"].Values["Chcode"].ToString().ToLower() == this.txtCode.Text.Trim().ToString().ToLower())
　　{
　　　　...
　　}

valicode.aspx.cs文件

protected void Page_Load(object sender, EventArgs e)
    {
        string chcode = "";
        //颜色列表，用于验证码，噪线，躁点的绘制
        Color[] colors = { Color.Black, Color.Red, Color.Green, Color.Orange, Color.DarkBlue };
        //字体列表，用于验证码
        string[] font = { "Times New Roman", "MS MinCho", "Book Antiqua", "Gungsuh", "PMingLiU", "Impact" };
        //验证码的字符集，去掉容易混淆的字符
        char[] Character = { '2', '3', '4', '5', '6', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'J', 'K', 'L', 'M', 'N', 'P', 'R', 'S', 'T', 'W', 'X', 'Y' };
        //实例化一个随机对象
        Random random = new Random();
        //随机生成验证码
        for (int i = 0; i < 4; i++)
        {
            chcode += Character[random.Next(Character.Length)];
        }

        //保存验证码 Cookie
        HttpCookie anycookie = new HttpCookie("ValidateCookie");
        anycookie.Values.Add("Chcode", chcode);
        HttpContext.Current.Response.Cookies["ValidateCookie"].Values["Chcode"] = chcode;

        Bitmap bmp = new Bitmap(100, 30);
        Graphics g = Graphics.FromImage(bmp);
        g.Clear(Color.White);
        //画噪音线
        for (int i = 0; i < 5; i++)
        {
            int x1 = random.Next(100);
            int y1 = random.Next(30);
            int x2 = random.Next(100);
            int y2 = random.Next(30);
            Color clr = colors[random.Next(colors.Length)];
            g.DrawLine(new Pen(clr), x1, y1, x2, y2);

        }
        //画验证码字符串
        for (int i = 0; i < chcode.Length; i++)
        {
            string fontsytle = font[random.Next(font.Length)];
            Font fnt = new Font(fontsytle, 16);
            Color fcolor = colors[random.Next(colors.Length)];
            g.DrawString(chcode[i].ToString(), fnt, new SolidBrush(fcolor), i * 20 + 20, 6);
        }
        //画噪点
        for (int i = 0; i < 100; i++)
        {
            int x = random.Next(bmp.Width);
            int y = random.Next(bmp.Height);
            Color fcolor = colors[random.Next(colors.Length)];
            bmp.SetPixel(x, y, fcolor);
        }

        //清除该页输出缓存，设置该页无缓存
        Response.Buffer = true;
        Response.ExpiresAbsolute = System.DateTime.Now.AddMilliseconds(0);
        Response.Expires = 0;
        Response.CacheControl = "no-cache";
        Response.AppendHeader("Pragma", "No-Cache");

        //把验证码图片写入到内存中，并以图片格式输出（"imgae/png"）;
        MemoryStream stream = new MemoryStream();
        try
        {
            bmp.Save(stream, ImageFormat.Png);
            Response.ClearContent();
            Response.ContentType = "Image/png";
            Response.BinaryWrite(stream.ToArray());
        }
        finally
        {
            bmp.Dispose();
            g.Dispose();

        }
    }