验证码比较的问题 各位帮看看怎么写

[frank2828]

下面是我的验证码详细代码，我抄别人的：
我想比较文本框和验证码数字是否相等，高不定啊，各位大侠帮我看看怎么写
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Text;
using System.Drawing.Drawing2D;
using System.Drawing;
using System.IO;
using System.Drawing.Imaging;

public partial class manage_yanzhengma : System.Web.UI.Page
{
private string code;
private const int ImageHeigth = 22; //验证码图片的高度
private const double ImageLengthBase = 12.5; //验证码图片中每个字符的宽度
private const int ImageLineNumber = 25; //噪音线的数量
private const int ImagePointNumber = 100; //噪点的数量
private int length;
public static string VALIDATECODEKEY; //此处用来保存验证码到Session的Key的名称

//静态构造函数初始化验证码在Session中的Key名称
static manage_yanzhengma()
{
VALIDATECODEKEY = "VALIDATECODEKEY";
}

//设置验证码的长度和内容
public manage_yanzhengma()
{
this.length = 4;
this.code = string.Empty;
}

/// <summary>
/// 产生随机的验证码并加入Session
/// </summary>
/// <param name="length">验证码长度</param>
/// <returns></returns>
public string CreateCode(int length)
{
if (length <= 0)
{
return string.Empty;
}
Random random = new Random();
StringBuilder builder = new StringBuilder();
//产生随机的验证码并拼接起来
for (int i = 0; i < length; i++)
{
builder.Append(random.Next(0, 10));
}
this.code = builder.ToString();
this.Session[VALIDATECODEKEY] = this.code;
return this.code;
}

/// <summary>
/// 根据长度产生验证码
/// 并将验证码画成图片
/// </summary>
/// <param name="length">验证码长度</param>
public void CreateValidateImage(int length)
{
this.code = this.CreateCode(length);
this.CreateValidateImage(this.code);
}
/// <summary>
/// 根据产生的验证码生成图片
/// </summary>
/// <param name="code">验证码</param>
public void CreateValidateImage(string code)
{
if (!string.IsNullOrEmpty(code))
{
this.Session[VALIDATECODEKEY] = code;
//初始化位图Bitmap对象，指定图片对象的大小(宽,高)
Bitmap image = new Bitmap((int)Math.Ceiling((double)(code.Length * ImageLengthBase)), ImageHeigth);
//初始化一块画布
Graphics graphics = Graphics.FromImage(image);
Random random = new Random();
try
{
int num5;
graphics.Clear(Color.White);
//绘制噪音线
for (num5 = 0; num5 < ImageLineNumber; num5++)
{
int num = random.Next(image.Width);
int num3 = random.Next(image.Height);
int num2 = random.Next(image.Width);
int num4 = random.Next(image.Height);
graphics.DrawLine(new Pen(Color.Silver), num, num3, num2, num4);
}
//验证码字体样式
Font font = new Font("Tahoma", 12, FontStyle.Italic | FontStyle.Bold);
LinearGradientBrush brush = new LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height), Color.Blue, Color.DarkRed, 1.2f, true);
//绘制验证码到画布
graphics.DrawString(code, font, brush, (float)2, (float)2);
//绘制噪点
for (num5 = 0; num5 < ImagePointNumber; num5++)
{
int x = random.Next(image.Width);
int y = random.Next(image.Height);
image.SetPixel(x, y, Color.FromArgb(random.Next()));
}
graphics.DrawRectangle(new Pen(Color.Silver), 0, 0, image.Width - 1, image.Height - 1);
MemoryStream stream = new MemoryStream();
//保存图片
image.Save(stream, ImageFormat.Gif);
base.Response.ClearContent();
base.Response.ContentType = "image/Gif";
base.Response.BinaryWrite(stream.ToArray());
}
finally
{
graphics.Dispose();
image.Dispose();
}
}
}
protected override void OnLoad(EventArgs e)
{
this.CreateValidateImage(this.length);
}

// Properties
public string Code
{
get
{
return this.Code;
}
}
public int Length
{
get
{
return this.length;
}
set
{
this.length = value;
}
}
}


我在登陆后台这样比较的
if (txtYanZhengMa.Text.Trim() != Session["VALIDATECODEKEY"].ToString())
{
Page.ClientScript.RegisterClientScriptBlock(typeof(string), "msg", "<script>alert('验证码错误')</script>");
}

结果没有实现限制效果，各位高手 看看他的验证码 看看我该怎么写呢