asp.net 生成中文验证码

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Text;
using System.Drawing;

public partial class Member_checkcode : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        //调用函数产生4个随机中文汉字编码
        string randomcode = CreateRegionCode(4);
        Session["ValidNum"] = randomcode;
        this.CreateImage(randomcode);
    }
    /**/
    /// <summary>
    /// 中文
    /// </summary>
    /// <param name="strlength"></param>
    /// <returns></returns>
    public string 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);

        }

        //获取GB2312编码页（表）
        Encoding gb = Encoding.GetEncoding("gb2312");

        //根据汉字编码的字节数组解码出中文汉字
        string strResult = "";
        for (int i = 0; i < strlength; i++)
        {
            strResult += gb.GetString((byte[])Convert.ChangeType(bytes[i], typeof(byte[])));
        }

        return strResult;
    }

    /**/
    /// <summary>
    /// 创建随机码图片
    /// </summary>
    /// <param name="randomcode">随机码</param>
    private void CreateImage(string randomcode)
    {
        int randAngle = 30; //随机转动角度
        int mapwidth = (int)(randomcode.Length * 28);
        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(22, 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();
    }

}

使用验证码的前台

 <tr><td align="right">   验&nbsp;证&nbsp;码&nbsp;<span class="red">*</span></td><td> <label>
                                        <input type="text" name="txtValidNum" id="txtValidNum" class="int6" />
                                    </label> <img alt="" id="imgsrc" src="checkcode.aspx" onclick="imgchange()" style="cursor: pointer;" />
                                    <label onclick="imgchange()" style="cursor: pointer;">
                                    图片验证码看不清，换一张</label></td></tr>

使用的js判断

 function imgchange()
    {
       document.getElementById("imgsrc").src="checkcode.aspx?"+new Date;
    }

在使用到验证码的地方后台进行判断

 if (Request["txtValidNum"].Trim() != Session["ValidNum"].ToString())
        {
            __GotoWebMsg("验证码错误！");
            return;
        }