生成汉字验证码

C#代码：

using System.Text;
using System.Drawing;


public partial class Default3 : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {


        CreateCheckCodeImage(GetString(4));
        
    }
    private object[] CreateString(int strlenght)
    { 
        string[] str=new string[16] {"0","1","2","3","4","5","6","7","8","9","a","b","c","d","e","f"};
            Random ran=new Random ();
        object [] bytes=new object [strlenght ];
        for (int i=0;i<strlenght ;i++)
        {
        int ran1=ran.Next (11,14);
            string str1=str [ran1].Trim ();
            ran = new Random(ran1 * unchecked((int)DateTime.Now.Ticks) + i);
            int ran2;
            if (ran1 == 13)
            {
                ran2 = ran.Next(0, 7);

            }
            else
            {
                ran2 = ran.Next(0,16);
            }
            string str2 = str[ran2].Trim();
            ran = new Random(ran2 * unchecked((int)DateTime.Now.Ticks) + i);
            int ran3 = ran.Next(10,16);
            string str3 = str[ran3].Trim();
            ran = new Random(ran3 * unchecked((int)DateTime.Now.Ticks) + i);
            int ran4;
            if (ran3 == 10)
            {
                ran4 = ran.Next(1, 16);
            }
            else if (ran3 == 15)
            {
              ran4 = ran.Next(0, 15);
            }
            else
            { 
               ran4 = ran.Next(0, 16);
            }        
            string str4 = str[ran4].Trim();
            byte byte1 = Convert.ToByte(str1 + str2, 16);
            byte byte2 = Convert.ToByte(str3 + str4, 16);
            byte [] stradd=new byte []{byte1,byte2 };
            bytes.SetValue(stradd, i);

        }
        return bytes; 
    }
    private string GetString(int length)
    {
        Encoding gb = Encoding.GetEncoding("gb2312");
        object[] bytes = CreateString(length);
        string str1 = gb.GetString((byte[])Convert.ChangeType(bytes[0], typeof(byte[])));
        string str2 = gb.GetString((byte[])Convert.ChangeType(bytes[1], typeof(byte[])));
        string str3 = gb.GetString((byte[])Convert.ChangeType(bytes[2], typeof(byte[])));
        string str4 = gb.GetString((byte[])Convert.ChangeType(bytes[3], typeof(byte[])));
        string str = str1 + str2 + str3 + str4;

        Response.Cookies.Add(new HttpCookie ("CheckCode",str ));
        return str;
    }

    private void CreateCheckCodeImage(string checkCode)
    {
        if (checkCode == null || checkCode.Trim() == string.Empty)
            return;
        System.Drawing.Bitmap image = new System.Drawing.Bitmap((int)Math.Ceiling((checkCode.Length * 21.5)), 22);
        Graphics g = Graphics.FromImage(image);

        try
        {//生成随机生成器             
            Random random = new Random();
            g.Clear(Color.White);
            //画图片的背景噪音线   
            for (int i = 0; i < 25; 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);
            }
            Font font = new System.Drawing.Font("Arial", 12, (System.Drawing.FontStyle.Bold));
            System.Drawing.Drawing2D.LinearGradientBrush brush = new System.Drawing.Drawing2D.LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height), Color.Blue, Color.DarkRed, 1.2f, true);
            g.DrawString(checkCode, font, brush, 2, 2);
            //画图片的前景噪音点   
            for (int i = 0; i < 100; 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.ContentType = "image/gif";
            Response.BinaryWrite(ms.ToArray());
        }
        catch (Exception ms)
        {

            Response.Write(ms.Message);
        }
        finally
        {
            g.Dispose();
            image.Dispose();
        }
    }  

javascript代码：

<script type="text/javascript">   
       function change() {   
           var imgNode = document.getElementById("vimg");   
           imgNode.src = "Code.aspx?t=" + (new Date()).valueOf();  // 这里加个时间的参数是为了防止浏览器缓存的问题   
       }   
   </script>  

html代码：

<asp:Image ID="vimg" runat="server" Height ="18px" Width ="60px" src="Code.aspx" /><input type="button" value="换一张图片" onclick="change()" />