使用C#生成验证码图片，然后在网页中直接使用，很方便的用法。

using System;using System.Drawing;using System.Drawing.Imaging;using System.Web.UI;using System.Drawing.Drawing2D;using System.IO;/// 
/// 生成验证码的类/// 
public class ValidateCode{    public ValidateCode()    {    }    /// 
    /// 验证码的最大长度    /// 
    public int MaxLength    {        get { return 10; }    }    /// 
    /// 验证码的最小长度    /// 
    public int MinLength    {        get { return 1; }    }    /// 
    /// 生成验证码    /// 
    /// 指定验证码的长度    /// 
        public string CreateValidateCode(int length)    {        int[] randMembers = new int[length];        int[] validateNums = new int[length];        string validateNumberStr = "";        //生成起始序列值        int seekSeek = unchecked((int)DateTime.Now.Ticks);        Random seekRand = new Random(seekSeek);        int beginSeek = (int)seekRand.Next(0, Int32.MaxValue - length * 10000);        int[] seeks = new int[length];        for (int i = 0; i < length; i++)        {            beginSeek += 10000;            seeks[i] = beginSeek;        }        //生成随机数字        for (int i = 0; i < length; i++)        {            Random rand = new Random(seeks[i]);            int pownum = 1 * (int)Math.Pow(10, length);            randMembers[i] = rand.Next(pownum, Int32.MaxValue);        }        //抽取随机数字        for (int i = 0; i < length; i++)        {            string numStr = randMembers[i].ToString();            int numLength = numStr.Length;            Random rand = new Random();            int numPosition = rand.Next(0, numLength - 1);            validateNums[i] = Int32.Parse(numStr.Substring(numPosition, 1));        }        //生成验证码        for (int i = 0; i < length; i++)        {            validateNumberStr += validateNums[i].ToString();        }        return validateNumberStr;    }    /// 
    /// 创建验证码的图片    /// 
    /// 要输出到的page对象    /// 验证码    public byte[] CreateValidateGraphic(string validateCode)    {        Bitmap image = new Bitmap((int)Math.Ceiling(validateCode.Length * 12.0), 24);        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);            //画图片的干扰线            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 Font("Arial", 12, (FontStyle.Bold | FontStyle.Italic));            LinearGradientBrush brush = new LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height),             Color.Blue, Color.DarkRed, 1.2f, true);            g.DrawString(validateCode, font, brush, 3, 2);            //画图片的前景干扰点            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);            //保存图片数据            MemoryStream stream = new MemoryStream();            image.Save(stream, ImageFormat.Jpeg);            //输出图片流            return stream.ToArray();        }        finally        {            g.Dispose();            image.Dispose();        }    }    /// 
    /// 得到验证码图片的长度    /// 
    /// 验证码的长度    /// 
        public static int GetImageWidth(int validateNumLength)    {        return (int)(validateNumLength * 12.0);    }    /// 
    /// 得到验证码的高度    /// 
    /// 
        public static double GetImageHeight()    {        return 22.5;    }}