/// <summary>
/// 验证码生成类
/// </summary>
public class verify_code : IHttpHandler, IRequiresSessionState
{
 public void ProcessRequest(HttpContext context)
 {
  int codeW = 80;
  int codeH = 22;
  int fontSize = 16;
  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", "Verdana", "Arial", "Gungsuh", "Impact" };
  //验证码的字符集，去掉了一些容易混淆的字符 
  char[] character = { '0', '1', '2', '3', '4', '5', '6', '8', '9' };
  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)];
  }
  //写入Session
  context.Session["sys_verify_code"] = chkCode;
  //创建画布
  Bitmap bmp = new Bitmap(codeW, codeH);
  Graphics g = Graphics.FromImage(bmp);
  g.Clear(Color.White);
  //画噪线 
  for (int i = 0; i < 4; i++)
  {
   int x1 = rnd.Next(codeW);
   int y1 = rnd.Next(codeH);
   int x2 = rnd.Next(codeW);
   int y2 = rnd.Next(codeH);
   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, fontSize);
   Color clr = color[rnd.Next(color.Length)];
   g.DrawString(chkCode[i].ToString(), ft, new SolidBrush(clr), (float)i * 18 + 2, (float)0);
  }
  //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 
  context.Response.Buffer = true;
  context.Response.ExpiresAbsolute = System.DateTime.Now.AddMilliseconds(0);
  context.Response.Expires = 0;
  context.Response.CacheControl = "no-cache";
  context.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);
   context.Response.ClearContent();
   context.Response.ContentType = "image/Png";
   context.Response.BinaryWrite(ms.ToArray());
  }
  finally
  {
   //显式释放资源 
   bmp.Dispose();
   g.Dispose();
  }
 }
 
 public bool IsReusable
 {
  get
  {
   return false;
  }
 }
}

using System;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;
using System.Web;
 
public partial class image : System.Web.UI.Page
{
 protected void Page_Load(object sender, EventArgs e)
 {
  string tmp = RndNum(4);
  HttpCookie a = new HttpCookie("ImageV", tmp);
  Response.Cookies.Add(a);
  this.ValidateCode(tmp);
 }
 
 private void ValidateCode(string VNum)
 {
  Bitmap Img = null;
  Graphics g = null;
  MemoryStream ms = null;
  int gheight = VNum.Length * 12;
  Img = new Bitmap(gheight, 25);
  g = Graphics.FromImage(Img);
  //背景颜色
  g.Clear(Color.White);
  //文字字体
  Font f = new Font("Arial Black", 10);
  //文字颜色
  SolidBrush s = new SolidBrush(Color.Black);
  g.DrawString(VNum, f, s, 3, 3);
  ms = new MemoryStream();
  Img.Save(ms, ImageFormat.Jpeg);
  Response.ClearContent();
  Response.ContentType = "image/Jpeg";
  Response.BinaryWrite(ms.ToArray());
 
  g.Dispose();
  Img.Dispose();
  Response.End();
 }
 
 private string RndNum(int VcodeNum)
 {
  string Vchar = "0,1,2,3,4,5,6,7,8,9,a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p" +
   ",q,r,s,t,u,v,w,x,y,z";
  string[] VcArray = Vchar.Split(new Char[] { ',' });
  string VNum = "";
  int temp = -1;
 
  Random rand = new Random();
 
  for (int i = 1; i < VcodeNum + 1; i++)
  {
   if (temp != -1)
   {
    rand = new Random(i * temp * unchecked((int)DateTime.Now.Ticks));
   }
 
   int t = rand.Next(35);
   if (temp != -1 && temp == t)
   {
    return RndNum(VcodeNum);
   }
   temp = t;
   VNum += VcArray[t];
  }
  return VNum;
 }
 
}