------生成方法一

pageload（object sender, eventarges e）

{

string chkCode = string.Empty;
        //颜色列表，用于验证码、噪线、噪点 
        Color[] color = { Color.Black, Color.Red, Color.Blue, Color.Green, Color.Orange, Color.Brown, Color.Brown, 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，，去掉了一些容易混淆的字符 
        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‘ };
        Random rnd = new Random();
        //生成验证码字符串 
        for (int i = 0; i < 4; i++)
        {
            chkCode += character[rnd.Next(character.Length)];
        }
        Bitmap bmp = new Bitmap(100, 40);
        Graphics g = Graphics.FromImage(bmp);
        g.Clear(Color.White);
        //画噪线 
        for (int i = 0; i < 10; i++)
        {
            int x1 = rnd.Next(100);
            int y1 = rnd.Next(40);
            int x2 = rnd.Next(100);
            int y2 = rnd.Next(40);
            Color clr = color[rnd.Next(color.Length)];
            g.DrawLine(new Pen(clr), x1, y1, x2, y2);
        }
        //画验证码字符串 
        for (int i = 0; i < chkCode.Length; i++)
        {
            string fnt = font[rnd.Next(font.Length)];
            Font ft = new Font(fnt, 18);
            Color clr = color[rnd.Next(color.Length)];
            g.DrawString(chkCode[i].ToString(), ft, new SolidBrush(clr), (float)i * 20 + 8, (float)8);
        }
        //画噪点 
        for (int i = 0; i < 100; i++)
        {
            int x = rnd.Next(bmp.Width);
            int y = rnd.Next(bmp.Height);
            Color clr = color[rnd.Next(color.Length)];
            bmp.SetPixel(x, y, clr);
        }
        //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");
        //将验证码图片写入内存流，并将其以 "image/Png" 格式输出 
        MemoryStream ms = new MemoryStream();
        try
        {
            bmp.Save(ms, ImageFormat.Png);
            Response.ClearContent();
            Response.ContentType = "image/Png";
            //Response.BinaryWrite(ms.ToArray());            
            
        }
        finally
        {
            //显式释放资源 
            bmp.Dispose();
            g.Dispose();
        }

}

------生成方法二

<%@ WebHandler Language="C#" %>

using System;
using System.Web;
using System.Drawing;