protected void Page_Load(object sender, EventArgs e)

    {

        //生成验证码图片的基本步骤

        string checkCode = "新年快乐";

        //定义画布大小

        System.Drawing.Bitmap image = new System.Drawing.Bitmap((int)Math.Ceiling((checkCode.Length * 20.5)), );

        //指定绘制类型

        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 = ; i < ; 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.Black), x1, y1, x2, y2);

            }

            //指定字体/字号/样式

            Font font = new System.Drawing.Font("Arial", , (System.Drawing.FontStyle.Bold));

            //指定画笔, 线性渐变

            System.Drawing.Drawing2D.LinearGradientBrush brush = new System.Drawing.Drawing2D.LinearGradientBrush(new Rectangle(, , image.Width, image.Height), Color.Blue, Color.DarkRed, 1.2f, true);

            g.DrawString(checkCode, font, brush, , );

            //画图片的前景噪音点

            for (int i = ; i < ; 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), , , image.Width - , image.Height - );

            System.IO.MemoryStream ms = new System.IO.MemoryStream();

            //将绘制的图片以指定的格式保存到内存中

            image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);

            //清除缓存

            Response.ClearContent();

            //指定输出类型

            Response.ContentType = "image/Gif";

            //以二进制方式输出

            Response.BinaryWrite(ms.ToArray());

        }

        finally

        {

            g.Dispose();

            image.Dispose();

        }

    }

public partial class _Default : System.Web.UI.Page

{

    /// <summary>

    /// 生成随机数字符串, 并保存到Cookie中

    /// </summary>

    /// <returns></returns>

    private string GenerateCheckCode()

    {

        int number;

        char code;

        string checkCode = String.Empty;

        Random random = new Random();

        for (int i = ; i < ; i++)

        {

            number = random.Next();

            if (number %  == )

                code = (char)('' + (char)(number % ));

            else

                code = (char)('A' + (char)(number % ));

            checkCode += code.ToString();

        }

        Response.Cookies.Add(new HttpCookie("CheckCode", checkCode));

        return checkCode;

    }

    protected void Page_Load(object sender, EventArgs e)

    {

        string checkCode = GenerateCheckCode();

        System.Drawing.Bitmap image = new System.Drawing.Bitmap((int)Math.Ceiling((checkCode.Length * 13.3)), );

        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 = ; i < ; 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.Black), x1, y1, x2, y2);

            }

            Font font = new System.Drawing.Font("Arial", , (System.Drawing.FontStyle.Bold));

            System.Drawing.Drawing2D.LinearGradientBrush brush = new System.Drawing.Drawing2D.LinearGradientBrush(new Rectangle(, , image.Width, image.Height), Color.Blue, Color.DarkRed, 1.2f, true);

            g.DrawString(checkCode, font, brush, , );

            //画图片的前景噪音点

            for (int i = ; i < ; 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), , , image.Width - , image.Height - );

            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();

        }

    }

}