C#.Net 较完美随机验证码 [转]

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 WebApplication1.验证码
{
 ///  <summary>
 ///  完美随机验证码  0.10
 ///  Verion:0.10
 ///  Description:随机生成设定验证码，并随机旋转一定角度，字体颜色不同
 ///  </summary>

 public class ValidateCode : System.Web.UI.Page
 {
  private void Page_Load(object sender, System.EventArgs e)
  {
   string  randomcode  =  this.CreateRandomCode(4);
   Session["ValidateCode"]  =  randomcode;
   //ViewState["ValidateCode"]  =  randomcode;
   this.CreateImage(randomcode);

  }

  ///  <summary>
  ///  生成随机码
  ///  </summary>
  ///  <param  name="length">随机码个数</param>
  ///  <returns></returns>
  private  string  CreateRandomCode(int length)
  {
   int rand;
   char code;
   string randomcode = String.Empty;

   //生成一定长度的验证码
   System.Random random = new Random();
   for(int i=0;i<length;i++)
   {
    rand = random.Next();

    if(rand%3 == 0)
    {
     code = (char)('A' + (char)(rand%26));
    }
    else
    {
     code = (char)('0' + (char)(rand%10));
    }

    randomcode += code.ToString();
   }
   return  randomcode;
  }
  
  ///  <summary>
  ///  创建随机码图片
  ///  </summary>
  ///  <param  name="randomcode">随机码</param>
  private  void  CreateImage(string randomcode)
  {
   int randAngle = 45; //随机转动角度
   int mapwidth = (int)(randomcode.Length * 23);
   Bitmap map = new Bitmap(mapwidth,28);//创建图片背景
   Graphics graph = Graphics.FromImage(map);
   graph.Clear(Color.AliceBlue);//清除画面，填充背景
   graph.DrawRectangle(new Pen(Color.Black,0),0,0,map.Width-1,map.Height-1);//画一个边框
   //graph.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;//模式
                       

   Random rand = new Random();

   //背景噪点生成
   Pen blackPen = new Pen(Color.LightGray,0);
   for (int i=0;i<50;i++)
   {
           int x = rand.Next(0,map.Width);
           int y = rand.Next(0,map.Height);
           graph.DrawRectangle(blackPen,x,y,1,1);
   }

   //验证码旋转，防止机器识别
   char[] chars = randomcode.ToCharArray();//拆散字符串成单字符数组

   //文字距中
   StringFormat format = new StringFormat(StringFormatFlags.NoClip);
   format.Alignment = StringAlignment.Center;
   format.LineAlignment = StringAlignment.Center;

   //定义颜色
   Color[] c = { Color.Black, Color.Red, Color.DarkBlue, Color.Green, Color.Orange, Color.Brown, Color.DarkCyan, Color.Purple };
   //定义字体
   string[] font = { "Verdana", "Microsoft Sans Serif", "Comic Sans MS", "Arial", "宋体" };

   for(int i=0;i<chars.Length;i++)
   {
    int cindex = rand.Next(7);
    int findex = rand.Next(5);

    Font f = new System.Drawing.Font(font[findex],13,System.Drawing.FontStyle.Bold);//字体样式(参数2为字体大小)
    Brush b = new System.Drawing.SolidBrush(c[cindex]);

    Point dot = new Point(16,16);
    //graph.DrawString(dot.X.ToString(),fontstyle,new SolidBrush(Color.Black),10,150);//测试X坐标显示间距的
    float angle = rand.Next(-randAngle,randAngle);//转动的度数

    graph.TranslateTransform(dot.X,dot.Y);//移动光标到指定位置
    graph.RotateTransform(angle); 
                graph.DrawString(chars[i].ToString(),f,b,1,1,format);           
    //graph.DrawString(chars[i].ToString(),fontstyle,new SolidBrush(Color.Blue),1,1,format);
    graph.RotateTransform(-angle);//转回去
    graph.TranslateTransform(2,-dot.Y);//移动光标到指定位置
   }
   //graph.DrawString(randomcode,fontstyle,new SolidBrush(Color.Blue),2,2); //标准随机码
                       
   //生成图片
   System.IO.MemoryStream ms = new System.IO.MemoryStream();
   map.Save(ms,System.Drawing.Imaging.ImageFormat.Gif);
   Response.ClearContent();
   Response.ContentType = "image/gif";
   Response.BinaryWrite(ms.ToArray());
   graph.Dispose();
   map.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
 }
}