有人能给个验证码的例证吗?最好是5位的

有人能给个验证码的例子吗?最好是5位的.
有人有现成的吗?要下班了,很着急!谢谢了!

------解决方案--------------------------------------------------------
建CheckCode.aspx里加入方法

#region 生成随机数

private string GenerateCheckCode()
{
int number;
char code;
string checkCode = String.Empty;

System.Random random = new Random();

for(int i=0; i <5; i++)
{
number = random.Next();

if(number % 2 == 0)
code = (char)( '0 ' + (char)(number % 10));
else
code = (char)( 'A ' + (char)(number % 26));

checkCode += code.ToString();
}

Response.Cookies.Add(new HttpCookie( "CheckCode ", checkCode));

return checkCode;
}

#endregion 生成随机数

#region 随机画图

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 * 12.5)), 22);
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, y1, x2, y2);
}

Font font = new System.Drawing.Font( "Arial ", 12, (System.Drawing.FontStyle.Bold | System.Drawing.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(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());
}
finally
{
g.Dispose();
image.Dispose();
}
}

#endregion 随机画图

然后在PageLoad里面调用一下CreateCheckCodeImage(GenerateCheckCode())就可以了
------解决方案--------------------------------------------------------
using System;
using System.Data;
using System.Configuration;
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;

/// <summary>
/// randomCode 的摘要说明
/// </summary>
public class randomCode
{
public randomCode()
{
//
// TODO: 在此处添加构造函数逻辑
//
}
public string RandomNum(int n) //
{
string strchar = "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,V,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[] VcArray = strchar.Split( ', ');
string VNum = " "; //