using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Drawing;
using System.IO;

namespace SecurityCodePic
{
 public class DrawingSecurityCode
 {
  /// summary>
  /// 生成驗證碼，并返回
  /// /summary>
  /// returns>/returns>
  public string GetSecurityCode(int n)
  {
   string code = GenerateCheckCode(n);
   CreateCheckCodeImage(code);
   return code;
  }

  /// summary>
  /// 動態生成指定數目的隨機數或字母
  /// /summary>
  /// param name="num">整數/param>
  /// returns>返回驗證碼字符串/returns>
  private string GenerateCheckCode(int num)
  {
   int number;//定義變量
   char code;
   string checkCode = String.Empty; //空字符串，只讀
   Random random = new Random(); //定義隨機變量實例
   for (int i=0; i  num;i++ )
   {
    //利用for循環生成指定數目的隨機數或字母
    number = random.Next(); //返回一個小于指定的最大值的非負的隨機數 next有三個構造函數 
    if (number % 2 == 0)
    {//產生一個一位數
     code = (char)('0' + (char)(number % 10));
    }
    else
    { //產生一個大寫字母
     code = (char)('A'+(char)(number % 26));
    }
    checkCode += code.ToString();
   }
   return checkCode;
  }

  /// summary>
  /// 根據驗證碼字符串生成驗證碼圖片
  /// /summary>
  /// param name="checkCode">驗證碼字符串/param>
  private void CreateCheckCodeImage(string checkCode)
  {

   if (checkCode == null || checkCode.Trim() == String.Empty) return;
   // 引用System.Drawing類庫
   Bitmap myImage = new Bitmap(80, 30);//生成一個指定大小的位圖
   Graphics graphics = Graphics.FromImage(myImage); //從一個位圖生成一個畫布
   try
   {
    graphics.Clear(Color.White); //清除整個繪畫面并以指定的背景色填充,這里是把背景色設為白色
    Random random = new Random(); //實例化一個偽隨機數生成器

    //畫圖片的前景噪音點,這里有100個
    for (int i = 0; i  100; i++)
    {
     int x = random.Next(myImage.Width);
     int y = random.Next(myImage.Height);
     myImage.SetPixel(x, y, Color.FromArgb(random.Next()));//指定坐標為x,y處的像素的顏色
    }

    //畫圖片的背景噪音線,這里為2條
    for (int i = 0; i  2; i++)
    {
     int x1 = random.Next(myImage.Width);
     int x2 = random.Next(myImage.Width);
     int y1 = random.Next(myImage.Height);
     int y2 = random.Next(myImage.Height);
     graphics.DrawLine(new Pen(Color.Black), x1, y1, x2, y2); //繪制一條坐標x1,y1到坐標x2,y2的指定顏色的線條，這里的線條為黑色
    }

    Font font = new Font("Arial", 15, FontStyle.Bold); //定義特定的文本格式,這里的字體為Arial，大小為15,字體加粗
    //根據矩形、起始顏色和結束顏色以及方向角度產生一個LinearGradientBrush實例---線性漸變
    System.Drawing.Drawing2D.LinearGradientBrush brush =
     new System.Drawing.Drawing2D.LinearGradientBrush(
      new Rectangle(0, 0, myImage.Width, myImage.Height),//在坐標0,0處實例化一個和myImage同樣大小的矩形
      Color.Blue, Color.Red, 1.2f, true);
    //繪制文本字符串
    graphics.DrawString(checkCode, font, brush, 2, 2);

    //繪制有坐標對、寬度和高度指定的矩形---畫圖片的邊框線
    graphics.DrawRectangle(new Pen(Color.Silver), 0, 0, myImage.Width - 1, myImage.Height - 1);
    //創建其支持存儲器為內存的流
    MemoryStream ms = new MemoryStream();
    //將此圖像以指定格式保存到指定的流中
    myImage.Save(ms, System.Drawing.Imaging.ImageFormat.Gif); //這里是以gif的格式保存到內存中
    HttpContext.Current.Response.ClearContent(); //清除緩沖區流中的所有內容輸出
    HttpContext.Current.Response.ContentType = "image/Gif"; //獲取或設置輸出流的HTTP MIME類型
    HttpContext.Current.Response.BinaryWrite(ms.ToArray()); //將一個二進制字符串寫入HTTP輸出流
   }
   finally
   {
    //釋放占用資源
    graphics.Dispose();
    myImage.Dispose();
   }
  }
 }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace SecurityCodePic
{
 /// summary>
 /// SecurityCode1 的摘要說明
 /// /summary>
 public class SecurityCode1 : IHttpHandler
 {

  public void ProcessRequest(HttpContext context)
  {
   DrawingSecurityCode sc = new DrawingSecurityCode();
   string SecurityCode = sc.GetSecurityCode(6);
  }

  public bool IsReusable
  {
   get
   {
    return false;
   }
  }
 }
}

%@ Page Language="C#" AutoEventWireup="true" CodeBehind="SecurityCode_Test.aspx.cs" Inherits="SecurityCodePic.SecurityCode_Test" %>

!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

html xmlns="http://www.w3.org/1999/xhtml">
head runat="server">
 title>驗證碼的實現/title>
 style type="text/css">
 #VCodeImg { cursor: pointer;}
 /style>
/head>
body>
 form id="form1" runat="server">
 div>
 img id="VCodeImg" src="SecurityCode.ashx" alt="驗證碼" onclick="javascript:RefreshCode();" />
 /div>
 /form>
 script type="text/javascript">
  function RefreshCode() {
   var random = Math.random();
   var img = document.getElementById("VCodeImg");
   img.src = "SecurityCode.ashx?" + random; //加上無意義的隨機參數，瀏覽器才會認為是新地址，就會重新讀取數據
  }
 /script>
/body>
/html>