生成验证码

                  生成验证码
using System;
using System.Collections;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Web;
using System.Web.SessionState;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.HtmlControls;

namespace book
{
 /// <summary>
 /// Code 的摘要说明。
 /// </summary>
 public class Code : System.Web.UI.Page
 {
  private void Page_Load(object sender, System.EventArgs e)
  {
   // 在此处放置用户代码以初始化页面
   string checkCode = CreateRandomCode(4);
   Session["CheckCode"] = checkCode;
   CreateImage(checkCode);
  }
  private string CreateRandomCode(int codeCount)
  {

   // 函数功能:产生数字和字符混合的随机字符串
   string allChar = "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,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[] allCharArray = allChar.Split(',');
   string randomCode = "";
   int temp = -1;

   Random rand = new Random();
   for(int i = 0; i < codeCount; i++)
   {
    if(temp != -1)
    {
     rand = new Random(i*temp*((int)DateTime.Now.Ticks));
    }
    int t = rand.Next(35);
    if(temp == t)
    {
     return CreateRandomCode(codeCount);
    }
    temp = t;
    randomCode += allCharArray[t];
   }
   return randomCode;
  }

  private void CreateImage(string checkCode)
  {

   // 生成图象验证码函数
   int iwidth = (int)(checkCode.Length * 11.5);
   System.Drawing.Bitmap image = new System.Drawing.Bitmap(iwidth, 20);
   Graphics g = Graphics.FromImage(image);
   Font f = new System.Drawing.Font("Arial", 10, System.Drawing.FontStyle.Bold);
   Brush b = new System.Drawing.SolidBrush(Color.Azure);//字母白色
   //g.FillRectangle(new System.Drawing.SolidBrush(Color.Blue),0,0,image.Width, image.Height);
   g.Clear(Color.Gray);//背景灰色
   g.DrawString(checkCode, f, b, 3, 3);

   Pen blackPen = new Pen(Color.Black, 0);
   Random rand = new Random();

   System.IO.MemoryStream ms = new System.IO.MemoryStream();
   image.Save(ms,System.Drawing.Imaging.ImageFormat.Jpeg);
   Response.ClearContent();
   Response.ContentType = "image/Jpeg";
   Response.BinaryWrite(ms.ToArray());
   g.Dispose();
   image.Dispose();

  }

  #region Web 窗体设计器生成的代码
  override protected void OnInit(EventArgs e)
  {
   //
   // CODEGEN: 该调用是 ASP.NET Web 窗体设计器所必需的。
   //
   InitializeComponent();
   base.OnInit(e);
  }
  
  /// <summary>
  /// 设计器支持所需的方法 - 不要使用代码编辑器修改
  /// 此方法的内容。
  /// </summary>
  private void InitializeComponent()
  {   
   this.Load += new System.EventHandler(this.Page_Load);
  }
  #endregion
 }
}

前台的实现
private void Page_Load(object sender, System.EventArgs e)
  {
   // 在此处放置用户代码以初始化页面
   string VNum = "";
   if (Session["CheckCode"]!=null)
   {
    VNum=Session["CheckCode"].ToString();

    ViewState["VNum"]=VNum;
    Session["CheckCode"]=null;

   }
  }