C#.NET如何生成验证码呢？？源文件给你看！

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.Drawing;
using System.Drawing.Drawing2D;
using System.IO;
using System.Drawing.Imaging;

public partial class CheckCode : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
CreateCheckCodeImage(GenerateCheckCode());
}

private string GenerateCheckCode()
{
int number;
string strCode = "";// string.Empty;

//随机数种子

Random random = new Random();

for (int i = 0; i < 4; i++)//校验码长度为4
{
//随机数的整数
number = random.Next(10);
//字符从0-9,//A-Z中随机产生对应的ASCII码分别为
//48-57,//65-90
//number = number % 36;
//if (number < 10)
//{
//    number += 48;
//}
//else
//{
//    number += 48; //number += 55;
//}
number += 48;
//strCode += ((char)number).ToString();
strCode += ((char)number).ToString();
}
//在Cookie中保存校验码
//Response.Cookies.Add(new HttpCookie("CheckCode", strCode));
//在Session中保存校验码
Session["CheckCode"] = strCode;
return strCode;
}
///<summary>
///根据校验码输出图片
///</summary>
///<param name="checkCode">产生的随机校验码</param>

private void CreateCheckCodeImage(string checkCode)
{
//若校验码为空,则直接返回
if (checkCode == null || checkCode.Trim() == String.Empty)
return;
//根据校验码的长度确定输出图片的长度
System.Drawing.Bitmap image = new System.Drawing.Bitmap((int)Math.Ceiling(Convert.ToDecimal(checkCode.Length * 15)), 20);
//创建Graphics对象
Graphics g = Graphics.FromImage(image);

try
{
//生成随机数种子
Random random = new Random();

//清空图片背景色
g.Clear(Color.White);

//画图片的背景噪音线10条

for (int i = 0; i < 10; i++)
{
//噪音线起点坐标(x1,y1),终点坐标(x2,y2)

int x1 = random.Next(image.Width);
int x2 = random.Next(image.Width);
int y1 = random.Next(image.Height);
int y2 = random.Next(image.Height);

//用银色线画出噪音线
g.DrawLine(new Pen(Color.Silver), x1, y1, x2, y2);
}

//输出图片中校验码的字体:12号Arial,粗斜体

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

//线性渐变画刷
LinearGradientBrush brush = new LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height), Color.Blue, Color.Purple, 1.2f, true);
g.DrawString(checkCode, font, brush, 2, 2);

//画图片的前景噪音点50个
for (int i = 0; i < 50; 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.SaddleBrown), 0, 0, image.Width - 1, image.Height - 1);

//创建内存流用于输出图片
//using (MemoryStream ms = new MemoryStream())
//{
////图片格式指定为png
//    image.Save(ms, ImageFormat.Png);

////清除缓冲区流中的所有输出
//    Response.ClearContent();

////输出流的HHT MIME类型设置为"image/png"
//    Response.ContentType = "image/Png";

////输出的图片的二进制流
//    Response.BinaryWrite(ms.ToArray());
//}

//清除缓冲区流中的所有输出
Response.ClearContent();

//输出流的HHT MIME类型设置为"image/png"
Response.ContentType = "image/Png";

//图片格式指定为Jpeg
image.Save(Response.OutputStream, ImageFormat.Jpeg);

}
finally
{
//释放Bitmap对象和Graphics对象
g.Dispose();
image.Dispose();
}

}
}