.net实现验证码功能

 一、验证码简介
　　验证码功能一般是用于防止批量注册的，不少网站为了防止用户利用机器人自动注册、登录、灌水，都采用了验证码技术。所谓验证码，就是将一串随机产生的数字或字母或符号或文字，生成一幅图片， 图片里加上一些干扰象素（防止OCR），由用户肉眼识别其中的验证码信息，输入表单提交网站验证，验证成功后才能使用某项功能。

　　常见的验证码有如下几种： 
　　1、纯数字验证码，一般为四位随机数字；
　　2、数字+字母验证码，一般从数字（0~9）和字母(A~Z和a~z)中随机抽出几个字符组成；
　　3、汉字验证码，相对而言，这种验证码比较少见一点，实现起来也相对复杂一些，但在不少网站中还是可以看到的；

　　二、验证码的实现
　　1、纯数字验证码的实现
　　纯数字验证码的实现相对比较简单，可通过以下两种方法来实现
　　（1）使用随机数方式，代码如下：　

         private  String GetRandomint( int  codeCount)
        {
            Random random  =   new  Random();
             string  min  =   "" ;
             string  max  =   "" ;
             for  ( int  i  =   0 ; i  <  codeCount; i ++ )
            {
                min  += " 1 " ;
                max += " 9 " ;
            }
                 return  (random.Next(Convert.ToInt32(min),Convert.ToInt32(max)).ToString());
        }

 　　(2)使用随机组合方式，代码如下：

         private   string  CreateRandomCode( int  codeCount)
        {
             string  allChar  =   " 0,1,2,3,4,5,6,7,8,9 " ; 
             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( 9 ); 
                 if  (temp  ==  t) 
                { 
                     return  CreateRandomCode(codeCount); 
                } 
                temp  =  t; 
                randomCode  +=  allCharArray[t]; 
            } 
             return  randomCode;
        }

　　2、数字+字母验证码的实现，代码如下：

         private   string  CreateRandomCode( int  codeCount)
        {
             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,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( 61 ); 
                 if  (temp  ==  t) 
                { 
                     return  CreateRandomCode(codeCount); 
                } 
                temp  =  t; 
                randomCode  +=  allCharArray[t]; 
            } 
             return  randomCode;
        }

　　3、汉字验证码的实现，代码如下： 

         /**/
         /*  
    此函数在汉字编码范围内随机创建含两个元素的十六进制字节数组，每个字节数组代表一个汉字，并将 
    四个字节数组存储在object数组中。 
    参数：strlength，代表需要产生的汉字个数 
     */
         public   static   object [] CreateRegionCode( int  strlength)
        {
             // 定义一个字符串数组储存汉字编码的组成元素 
             string [] rBase  =   new  String[ 16 ] {  " 0 " ,  " 1 " ,  " 2 " ,  " 3 " ,  " 4 " ,  " 5 " ,  " 6 " ,  " 7 " ,  " 8 " ,  " 9 " ,  " a " ,  " b " ,  " c " ,  " d " ,  " e " ,  " f "  };
            Random rnd  =   new  Random();
             // 定义一个object数组用来 
             object [] bytes  =   new   object [strlength];

             /**/
             /* 每循环一次产生一个含两个元素的十六进制字节数组，并将其放入bject数组中 
         每个汉字有四个区位码组成 
         区位码第1位和区位码第2位作为字节数组第一个元素 
         区位码第3位和区位码第4位作为字节数组第二个元素 
         */
             for  ( int  i  =   0 ; i  <  strlength; i ++ )
            {
                 // 区位码第1位 
                 int  r1  =  rnd.Next( 11 ,  14 );
                 string  str_r1  =  rBase[r1].Trim();

                 // 区位码第2位 
                rnd  =   new  Random(r1  *   unchecked (( int )DateTime.Now.Ticks)  +  i); // 更换随机数发生器的种子避免产生重复值 
                 int  r2;
                 if  (r1  ==   13 )
                {
                    r2  =  rnd.Next( 0 ,  7 );
                }
                 else
                {
                    r2  =  rnd.Next( 0 ,  16 );
                }
                 string  str_r2  =  rBase[r2].Trim();

                 // 区位码第3位 
                rnd  =   new  Random(r2  *   unchecked (( int )DateTime.Now.Ticks)  +  i);
                 int  r3  =  rnd.Next( 10 ,  16 );
                 string  str_r3  =  rBase[r3].Trim();

                 // 区位码第4位 
                rnd  =   new  Random(r3  *   unchecked (( int )DateTime.Now.Ticks)  +  i);
                 int  r4;
                 if  (r3  ==   10 )
                {
                    r4  =  rnd.Next( 1 ,  16 );
                }
                 else   if  (r3  ==   15 )
                {
                    r4  =  rnd.Next( 0 ,  15 );
                }
                 else
                {
                    r4  =  rnd.Next( 0 ,  16 );
                }
                 string  str_r4  =  rBase[r4].Trim();

                 // 定义两个字节变量存储产生的随机汉字区位码 
                 byte  byte1  =  Convert.ToByte(str_r1  +  str_r2,  16 );
                 byte  byte2  =  Convert.ToByte(str_r3  +  str_r4,  16 );
                 // 将两个字节变量存储在字节数组中 
                 byte [] str_r  =   new   byte [] { byte1, byte2 };

                 // 将产生的一个汉字的字节数组放入object数组中 
                bytes.SetValue(str_r, i);
            }
             return  bytes;
        }

　　 三、具体实例　
　　 (实例1)　

前台代码display.aspx
<!--

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--><body>
    <form id="form1" runat="server">
    <div>
       <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
        <asp:Image ID="Image1" runat="server" ImageUrl="png.aspx" /><br />
        <br />
       <asp:Button ID="Button2" runat="server" OnClick="Button2_Click" Text="Button" />
        <asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="True" OnSelectedIndexChanged="DropDownList1_SelectedIndexChanged">
            <asp:ListItem Value="3">默认</asp:ListItem>
            <asp:ListItem Value="1">文字</asp:ListItem>
            <asp:ListItem Value="2">数字</asp:ListItem>
            <asp:ListItem Value="3">混合</asp:ListItem>
        </asp:DropDownList></div>
    </form>
</body>

后台代码display.cs
<!--

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-->        protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
        {
            switch (DropDownList1.SelectedValue)
            {
                case "1":
                    Image1.ImageUrl = "png.aspx?aa=1";
                    break;
                case "2":
                    Image1.ImageUrl = "png.aspx?aa=2";
                    break;
                case "3":
                    Image1.ImageUrl = "png.aspx?aa=3";
                    break;
            }
        }
        protected void Button2_Click(object sender, EventArgs e)
        {
            if (TextBox1.Text == Session["gif"].ToString())
                Response.Write("OK,正确");
            else
                Response.Write("验证码不符合");
        }

后台代码png.cs
<!--

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-->    public partial class png : System.Web.UI.Page
    {         
        protected void Page_Load(object sender, EventArgs e)
        {
            switch (Request.QueryString["aa"])
            {
                case "1":
                    gif = stxt(10);
                    Session["gif"] = stxt(10);
                    break;
                case "2":
                    gif = GetRandomint(4);
                    Session["gif"] = GetRandomint(4);
                    break;
                case "3":
                    gif = CreateRandomCode(4);
                    Session["gif"] = CreateRandomCode(4);
                    break;
                default:
                    gif = CreateRandomCode(4);
                    Session["gif"] = CreateRandomCode(4);
                    break;
            }
            CreateImage(Session["gif"].ToString());
        }

        private String GetRandomint(int codeCount)
        {
            Random random = new Random();
            string min = "";
            string max = "";
            for (int i = 0; i < codeCount; i++)
            {
                min +="1";
                max+="9";
            }
                return (random.Next(Convert.ToInt32(min),Convert.ToInt32(max)).ToString());
        }
        /**/
        /* 
    此函数在汉字编码范围内随机创建含两个元素的十六进制字节数组，每个字节数组代表一个汉字，并将 
    四个字节数组存储在object数组中。 
    参数：strlength，代表需要产生的汉字个数 
    */
        public static object[] CreateRegionCode(int strlength)
        {
            //定义一个字符串数组储存汉字编码的组成元素 
            string[] rBase = new String[16] { "0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "a", "b", "c", "d", "e", "f" };
            Random rnd = new Random();
            //定义一个object数组用来 
            object[] bytes = new object[strlength];

            /**/
            /*每循环一次产生一个含两个元素的十六进制字节数组，并将其放入bject数组中 
         每个汉字有四个区位码组成 
         区位码第1位和区位码第2位作为字节数组第一个元素 
         区位码第3位和区位码第4位作为字节数组第二个元素 
        */
            for (int i = 0; i < strlength; i++)
            {
                //区位码第1位 
                int r1 = rnd.Next(11, 14);
                string str_r1 = rBase[r1].Trim();

                //区位码第2位 
                rnd = new Random(r1 * unchecked((int)DateTime.Now.Ticks) + i);//更换随机数发生器的种子避免产生重复值 
                int r2;
                if (r1 == 13)
                {
                    r2 = rnd.Next(0, 7);
                }
                else
                {
                    r2 = rnd.Next(0, 16);
                }
                string str_r2 = rBase[r2].Trim();

                //区位码第3位 
                rnd = new Random(r2 * unchecked((int)DateTime.Now.Ticks) + i);
                int r3 = rnd.Next(10, 16);
                string str_r3 = rBase[r3].Trim();

                //区位码第4位 
                rnd = new Random(r3 * unchecked((int)DateTime.Now.Ticks) + i);
                int r4;
                if (r3 == 10)
                {
                    r4 = rnd.Next(1, 16);
                }
                else if (r3 == 15)
                {
                    r4 = rnd.Next(0, 15);
                }
                else
                {
                    r4 = rnd.Next(0, 16);
                }
                string str_r4 = rBase[r4].Trim();

                //定义两个字节变量存储产生的随机汉字区位码 
                byte byte1 = Convert.ToByte(str_r1 + str_r2, 16);
                byte byte2 = Convert.ToByte(str_r3 + str_r4, 16);
                //将两个字节变量存储在字节数组中 
                byte[] str_r = new byte[] { byte1, byte2 };

                //将产生的一个汉字的字节数组放入object数组中 
                bytes.SetValue(str_r, i);
            }
            return bytes;
        }
        private string stxt(int num)
        {
            Encoding gb = Encoding.GetEncoding("gb2312");

            //调用函数产生10个随机中文汉字编码 
            object[] bytes = CreateRegionCode(num);
            string strtxt = "";

            //根据汉字编码的字节数组解码出中文汉字 
            for (int i = 0; i < num; i++)
            {
                strtxt += gb.GetString((byte[])Convert.ChangeType(bytes[i], typeof(byte[])));
            }
            return strtxt;
        }
        /// <summary>
        /// 这个是使用字母,数字混合
        /// </summary>
        /// <param name="VcodeNum"></param>
        /// <returns></returns>
        private string CreateRandomCode(int codeCount)
        {
            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,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(61);
                if (temp == t)
                {
                    return CreateRandomCode(codeCount);
                }
                temp = t;
                randomCode += allCharArray[t];
            }
            return randomCode;
        }

        private void CreateImage(string checkCode)
        {
            int iwidth = (int)(checkCode.Length * 20);
            System.Drawing.Bitmap image = new System.Drawing.Bitmap(iwidth, 25);
            Graphics g = Graphics.FromImage(image);
            Font f = new System.Drawing.Font("Arial", 10, System.Drawing.FontStyle.Bold);
            Brush b = new System.Drawing.SolidBrush(Color.White);
            //g.FillRectangle(new System.Drawing.SolidBrush(Color.Blue),0,0,image.Width, image.Height);    
            g.Clear(Color.Black);
            g.DrawString(checkCode, f, b, 3, 3);
            Pen blackPen = new Pen(Color.Black, 0);
            Random rand = new Random();
            //for (int i=0;i<5;i++)    
            //{        
            //    int y = rand.Next(image.Height);  
            //    g.DrawLine(blackPen,0,y,image.W

idth,y); 
            //}        
            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();
        }
    }

　　 (实例2):20101018续加

调用页面前台代码

<!--

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-->          < script  language ="Javascript" >
         function  Regist()
        {
             var  url  =   "" ;
            url  =   " /GZPI/Service/Registry/ViewProtocol.aspx " ;
            window.open(url);    
             return   false ;
        }
         function  LoginClick()
        {
             if (document.Login.UserName.value  ==   "" )
            {
                alert( " 用户名不能为空！ " );
                 return   false ;
            }
            document.Login.submit();
            document.Login.Password.value  =   "" ;
             return   false ;
        }
        
         function  f_refreshtype()
        {    
             var  Image1  =  document.getElementById( " IMGCheckCode " );
               if  (Image1  !=   null ) 
               {
                   Image1.src  =  Image1.src  +   " ? " ;
             }
        }        
         </ script >
                         < TABLE  cellSpacing ="0"  cellPadding ="5"  width ="100%"  border ="0" >
                             < TR >
                                 < TD  class ="fontblack"  align ="right"  width ="30%" > 用 户 名： </ TD >
                                 < TD  vAlign ="bottom"  align ="left"  width ="62%" >< input  id ="Text1"  style ="BORDER-RIGHT: #43a7e2 1px solid; BORDER-TOP: #43a7e2 1px solid; BACKGROUND: #fcfcfc; BORDER-LEFT: #43a7e2 1px solid; BORDER-BOTTOM: #43a7e2 1px solid"
                                        size ="13"  name ="UserName"  width ="100px" >
                                 </ TD >
                             </ TR >
                             < TR >
                                 < TD  class ="fontblack"  align ="right"  height ="23" > 密  &nbsp;&nbsp;&nbsp; 码： </ TD >
                                 < TD  vAlign ="bottom"  align ="left"  height ="23" >< input  id ="Password1"  style ="BORDER-RIGHT: #43a7e2 1px solid; BORDER-TOP: #43a7e2 1px solid; BACKGROUND: #fcfcfc; BORDER-LEFT: #43a7e2 1px solid; BORDER-BOTTOM: #43a7e2 1px solid"
                                        type ="password"  size ="13"  name ="Password"  width ="100px" >
                                 </ TD >
                             </ TR >
                             < TR >
                                 < TD  class ="fontblack"  align ="right"  height ="23" > 校 &nbsp; 验 码： </ TD >
                                 < TD  valign ="top"  align ="left"  height ="23" >< FONT  face ="宋体" >< INPUT  id ="CheckCode"  style ="BORDER-RIGHT: #43a7e2 1px solid; BORDER-TOP: #43a7e2 1px solid; BACKGROUND: #fcfcfc; BORDER-LEFT: #43a7e2 1px solid; BORDER-BOTTOM: #43a7e2 1px solid"
                                            width ="100px"  size ="13"  name ="CheckCode" > &nbsp; </ FONT >< a  style ="CURSOR: hand"  onclick ="f_refreshtype()"  title ="看不清楚?点击获取新的校验码!"  border ="0" >< IMG  id ="IMGCheckCode"  src ="../GenerateCheckCode.aspx" ></ a >
                                 </ TD >
                             </ TR >
                             < TR  vAlign ="bottom"  align ="center" >
                                 < TD  class ="dlbuttom"  colSpan ="2"  height ="23" >< input  id ="Image1"  style ="CURSOR: hand"  onclick ="return LoginClick();"  tabIndex ="3"  type ="image"
                                        height ="17"  width ="55"  src ="images/login.gif"  border ="0"  name ="OkButton" > &nbsp;&nbsp;&nbsp;
                                     < input  type ="image"  onClick ="return Regist();"  border ='0'  src ='images/zuce.gif'  width ='55'
                                         height ='17'  ID ="Image2"  NAME ="Image2" >
                                 </ TD >
                             </ TR >
                         </ TABLE >

 

调用页面后台代码

<!--

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-->     private void OK_Click(object sender, System.EventArgs e)
        {
            if (!CheckCodeSame(CheckCode.Text.Trim()))
            {                    
                System.Web.HttpContext.Current.Response.Write(" < Script  Language ='JavaScript' > window.alert( ' 校验码错误！请重新输入！ ' );window.close(); </ script > ");
                return;
            }        
            int userType = 1;
            try
            {
                userType = int.Parse(UserType.Text);
            }
            catch
            {
            }

            GatewayManager gateway = new GatewayManager(corpCode.Text,collegeCode.Text,chargeCode.Text,userName.Text,password.Text,userType);
            gateway.Login(this);
        }

        ///  < summary >
        /// 判断输入的校验码是否正确
        ///  </ summary >
        ///  < param  name ="checkCode" ></ param >
        ///  < returns ></ returns >
        public static bool CheckCodeSame(string checkCode)
        {
            bool bSame = false; ;

            if (HttpContext.Current.Session["CheckCode"] != null)
            {
                if (checkCode.ToUpper() == HttpContext.Current.Session["CheckCode"].ToString().ToUpper())
                {
                    bSame = true;
                }
            }
            return bSame;
        }

 

　　

生成验证码前台文件

<!--

Code highlighting produced by Actipro CodeHighlighter (freeware)
http://www.CodeHighlighter.com/

--> < HTML >
     < HEAD >
         < title > GenerateCheckCode </ title >
         < meta  name ="GENERATOR"  Content ="Microsoft Visual Studio .NET 7.1" >
         < meta  name ="CODE_LANGUAGE"  Content ="C#" >
         < meta  name ="vs_defaultClientScript"  content ="JavaScript" >
         < meta  name ="vs_targetSchema"  content ="http://schemas.microsoft.com/intellisense/ie5" >
     </ HEAD >
     < body >
         < form  id ="form1"  runat ="server" >
             < div >< FONT  face ="宋体" ></ FONT >
             </ div >
         </ form >
     </ body >
</ HTML >

 

生成验证码后台文件

<!--

Code highlighting produced by Actipro CodeHighlighter (freeware)
http://www.CodeHighlighter.com/

--> using  System;
using  System.Collections;
using  System.Web;
using  System.Web.UI;
using  System.Web.UI.WebControls;
using  System.Drawing;
using  System.Drawing.Drawing2D;


namespace  GZPI.Gateway
{
     ///   <summary>
     ///  GenerateCheckCode 的摘要说明。
     ///   </summary>
     public   class  GenerateCheckCode : 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
             this .CreateCheckCodeImage(GenerateCheckCodes( 4 ));
        }

         #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

         private   string  GenerateCheckCodes( int  iCount)
        {
             int  number;
             string  checkCode  =  String.Empty;
             int  iSeed  =  DateTime.Now.Millisecond;
            System.Random random  =   new  Random(iSeed);
             for  ( int  i  =   0 ; i  <  iCount; i ++ )
            {
                number  =  random.Next( 10 );
                checkCode  +=  number.ToString();
            }

            Session[ " CheckCode " ]  =  checkCode;
             return  checkCode;
        }



         private   void  CreateCheckCodeImage( string  checkCode)
        {
             if  (checkCode  ==   null   ||  checkCode.Trim()  ==  String.Empty)
                 return ;
             int  iWordWidth  =   15 ;
             int  iImageWidth  =  checkCode.Length  *  iWordWidth;
            Bitmap image  =   new  Bitmap(iImageWidth,  20 );
            Graphics g  =  Graphics.FromImage(image);
             try
            {
                 // 生成随机生成器 
                Random random  =   new  Random();
                 // 清空图片背景色 
                g.Clear(Color.White);

                 // 画图片的背景噪音点
                 for  ( int  i  =   0 ; i  <   20 ; i ++ )
                {
                     int  x1  =  random.Next(image.Width);
                     int  x2  =  random.Next(image.Width);
                     int  y1  =  random.Next(image.Height);
                     int  y2  =  random.Next(image.Height);
                    g.DrawLine( new  Pen(Color.Silver), x1, y1, x2, y2);
                }

                 // 画图片的背景噪音线 
                 for  ( int  i  =   0 ; i  <   2 ; i ++ )
                {
                     int  x1  =   0 ;
                     int  x2  =  image.Width;
                     int  y1  =  random.Next(image.Height);
                     int  y2  =  random.Next(image.Height);
                     if  (i  ==   0 )
                    {
                        g.DrawLine( new  Pen(Color.Gray,  2 ), x1, y1, x2, y2);
                    }
            
                }


                 for  ( int  i  =   0 ; i  <  checkCode.Length; i ++ )
                {

                     string  Code  =  checkCode[i].ToString();
                     int  xLeft  =  iWordWidth  *  (i);
                    random  =   new  Random(xLeft);
                     int  iSeed  =  DateTime.Now.Millisecond;
                     int  iValue  =  random.Next(iSeed)  %   4 ;
                     if  (iValue  ==   0 )
                    {
                        Font font  =   new  Font( " Arial " ,  13 , (FontStyle.Bold  |  System.Drawing.FontStyle.Italic));
                        Rectangle rc  =   new  Rectangle(xLeft,  0 , iWordWidth, image.Height);
                        LinearGradientBrush brush  =   new  LinearGradientBrush(rc, Color.Blue, Color.Red,  1.5f ,  true );
                        g.DrawString(Code, font, brush, xLeft,  2 );
                    }
                     else   if  (iValue  ==   1 )
                    {
                        Font font  =   new  System.Drawing.Font( " 楷体 " ,  13 , (FontStyle.Bold));
                        Rectangle rc  =   new  Rectangle(xLeft,  0 , iWordWidth, image.Height);
                        LinearGradientBrush brush  =   new  LinearGradientBrush(rc, Color.Blue, Color.DarkRed,  1.3f ,  true );
                        g.DrawString(Code, font, brush, xLeft,  2 );
                    }
                     else   if  (iValue  ==   2 )
                    {
                        Font font  =   new  System.Drawing.Font( " 宋体 " ,  13 , (System.Drawing.FontStyle.Bold));
                        Rectangle rc  =   new  Rectangle(xLeft,  0 , iWordWidth, image.Height);
                        LinearGradientBrush brush  =   new  LinearGradientBrush(rc, Color.Green, Color.Blue,  1.2f ,  true );
                        g.DrawString(Code, font, brush, xLeft,  2 );
                    }
                     else   if  (iValue  ==   3 )
                    {
                        Font font  =   new  System.Drawing.Font( " 黑体 " ,  13 , (System.Drawing.FontStyle.Bold  |  System.Drawing.FontStyle.Bold));
                        Rectangle rc  =   new  Rectangle(xLeft,  0 , iWordWidth, image.Height);
                        LinearGradientBrush brush  =   new  LinearGradientBrush(rc, Color.Blue, Color.Green,  1.8f ,  true );
                        g.DrawString(Code, font, brush, xLeft,  2 );
                    }
                }
                 ////// 画图片的前景噪音点 
                 // for (int i = 0; i < 8; i++)
                 // {
                 //     int x = random.Next(image.Width);
                 //     int y = random.Next(image.Height);
                 //     image.SetPixel(x, y, Color.FromArgb(random.Next()));
                 // }
                 // 画图片的边框线 
                g.DrawRectangle( new  Pen(Color.Silver),  0 ,  0 , image.Width  -   1 , image.Height  -   1 );
                System.IO.MemoryStream ms  =   new  System.IO.MemoryStream();
                image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
                Response.ClearContent();

                Response.BinaryWrite(ms.ToArray());
            }
             finally
            {
                g.Dispose();
                image.Dispose();
            }
        }
    }
}

 

　　四、效果图展示
　　验证码数字

　　验证码数字+字母

　　验证码汉字

转摘： http://www.cnblogs.com/dreamof/archive/2009/01/22/1379822.html