如何生成汉字验证码或字母数字混合验证码

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Drawing;
using System.Data;
using System.Text;

public partial class ValidateNum : System.Web.UI.Page
{

//生成纯汉字验证码
public void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
//获取GB2312编码页（表）
Encoding gb = Encoding.GetEncoding("gb2312");

//调用函数产生4个随机中文汉字编码
object[] bytes = CreateRegionCode(6);

//根据汉字编码的字节数组解码出中文汉字
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[])));

Session["ValidateNum"] = str1 + str2 + str3 + str4;//保存验证码
}
}

/*
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;
}

//生成图片
private void CreateImage(string validateNum)
{
if (validateNum == null || validateNum.Trim() == String.Empty)
return;
//生成BitMap图像
Bitmap image = new Bitmap(validateNum.Length*12+40,24);
Graphics g = Graphics.FromImage(image);
try
{
//生成随机生成器
Random random = new Random();
//清空图片背景颜色
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);
g.DrawLine(new Pen(Color.Silver), x1, x2, y1, y2);
}

Font font = new Font("Arial",12,(FontStyle.Bold | FontStyle.Italic));
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(validateNum, 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();

//将图像保存到指定的流
image.Save(ms,System.Drawing.Imaging.ImageFormat.Gif);
Response.ClearContent();
Response.ContentType = "image/Gif";
Response.BinaryWrite(ms.ToArray());
}

finally
{
g.Dispose();
image.Dispose();
}

}
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Drawing;
using System.Data;
using System.Text;

public partial class ValidateNum : System.Web.UI.Page
{
生成数字+字母混合验证码
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{

string validateNum = CreateRandomNum(4) ;//生成4个随机字符串
CreateImage(validateNum);//将生成的随机字符串绘成图片
Session["ValidateNum"] = validateNum;//保存验证码
}

}

//随机生成数字+字母字符串
private string CreateRandomNum(int NumCount)
{
string allChar = "2,3,4,5,6,7,8,9,A,B,C,D,F,G,H,J,K,L,Q,W,E,R,T,Y,U,I,O,P,Z,X,C,V,B,N,M";
string[] allCharArray = allChar.Split(',');//拆分成组
string randomNum = "";
int temp = -1; //记录上次随机数的数值，尽量避免产生几个相同的随机数

Random rand = new Random();
for (int i = 0; i < NumCount; i++)
{
if (temp !=-1)
{
rand = new Random(i * temp * ((int)DateTime.Now.Ticks));
}
int t = rand.Next(35);
if (temp==t)
{
return CreateRandomNum(NumCount);
}
temp = t;
randomNum += allCharArray[t];
}
return randomNum;
}

//生成图片
private void CreateImage(string validateNum)
{
if (validateNum == null || validateNum.Trim() == String.Empty)
return;
//生成BitMap图像
Bitmap image = new Bitmap(validateNum.Length*12+40,24);
Graphics g = Graphics.FromImage(image);
try
{
//生成随机生成器
Random random = new Random();
//清空图片背景颜色
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);
g.DrawLine(new Pen(Color.Silver), x1, x2, y1, y2);
}

Font font = new Font("Arial",12,(FontStyle.Bold | FontStyle.Italic));
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(validateNum, 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();

//将图像保存到指定的流
image.Save(ms,System.Drawing.Imaging.ImageFormat.Gif);
Response.ClearContent();
Response.ContentType = "image/Gif";
Response.BinaryWrite(ms.ToArray());
}

finally
{
g.Dispose();
image.Dispose();
}

}
}