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(yàn)證碼，并返回
  /// </summary>
  /// <returns></returns>
  public string GetSecurityCode(int n)
  {
   string code = GenerateCheckCode(n);
   CreateCheckCodeImage(code);
   return code;
  }

  /// <summary>
  /// 動(dòng)態(tài)生成指定數(shù)目的隨機(jī)數(shù)或字母
  /// </summary>
  /// <param name="num">整數(shù)</param>
  /// <returns>返回驗(yàn)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(jī)變量實(shí)例
   for (int i=0; i < num;i++ )
   {
    //利用for循環(huán)生成指定數(shù)目的隨機(jī)數(shù)或字母
    number = random.Next(); //返回一個(gè)小于指定的最大值的非負(fù)的隨機(jī)數(shù) next有三個(gè)構(gòu)造函數(shù) 
    if (number % 2 == 0)
    {//產(chǎn)生一個(gè)一位數(shù)
     code = (char)('0' + (char)(number % 10));
    }
    else
    { //產(chǎn)生一個(gè)大寫(xiě)字母
     code = (char)('A'+(char)(number % 26));
    }
    checkCode += code.ToString();
   }
   return checkCode;
  }

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

   if (checkCode == null || checkCode.Trim() == String.Empty) return;
   // 引用System.Drawing類(lèi)庫(kù)
   Bitmap myImage = new Bitmap(80, 30);//生成一個(gè)指定大小的位圖
   Graphics graphics = Graphics.FromImage(myImage); //從一個(gè)位圖生成一個(gè)畫(huà)布
   try
   {
    graphics.Clear(Color.White); //清除整個(gè)繪畫(huà)面并以指定的背景色填充,這里是把背景色設(shè)為白色
    Random random = new Random(); //實(shí)例化一個(gè)偽隨機(jī)數(shù)生成器

    //畫(huà)圖片的前景噪音點(diǎn),這里有100個(gè)
    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(biāo)為x,y處的像素的顏色
    }

    //畫(huà)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(biāo)x1,y1到坐標(biāo)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(jù)矩形、起始顏色和結(jié)束顏色以及方向角度產(chǎn)生一個(gè)LinearGradientBrush實(shí)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(biāo)0,0處實(shí)例化一個(gè)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(biāo)對(duì)、寬度和高度指定的矩形---畫(huà)圖片的邊框線
    graphics.DrawRectangle(new Pen(Color.Silver), 0, 0, myImage.Width - 1, myImage.Height - 1);
    //創(chuàng)建其支持存儲(chǔ)器為內(nèi)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(nèi)存中
    HttpContext.Current.Response.ClearContent(); //清除緩沖區(qū)流中的所有內(nèi)容輸出
    HttpContext.Current.Response.ContentType = "image/Gif"; //獲取或設(shè)置輸出流的HTTP MIME類(lèi)型
    HttpContext.Current.Response.BinaryWrite(ms.ToArray()); //將一個(gè)二進(jìn)制字符串寫(xiě)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(shuō)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(yàn)證碼的實(shí)現(xiàn)</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(yàn)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(wú)意義的隨機(jī)參數(shù)，瀏覽器才會(huì)認(rèn)為是新地址，就會(huì)重新讀取數(shù)據(jù)
  }
 </script>
</body>
</html>