identifyingcode.aspx里没有内容略。
identifyingcode.cs文件：
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.Imaging;
using System.IO;
public partial class identifyingcode : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
string tmp = RndNum(4);
HttpCookie a = new HttpCookie("ImageV", tmp);
Response.Cookies.Add(a);
this.ValidateCode(tmp);

}
private void ValidateCode(string VNum)
{
Bitmap Img = null;
Graphics g = null;
MemoryStream ms = null;

int gheight = VNum.Length * 12;
Img = new Bitmap(gheight, 25);
g = Graphics.FromImage(Img);
//背景颜色
g.Clear(Color.LightSteelBlue);
//文字字体
Font f = new Font("Arial Black", 10);
//文字颜色
SolidBrush s = new SolidBrush(Color.RoyalBlue);
g.DrawString(VNum, f, s, 3, 3);
ms = new MemoryStream();
Img.Save(ms, ImageFormat.Jpeg);
Response.ClearContent();
Response.ContentType = "images/Jpeg";
Response.BinaryWrite(ms.ToArray());
g.Dispose();
Img.Dispose();
Response.End();
}

private string RndNum(int VcodeNum)
{
string Vchar = "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";
string[] VcArray = Vchar.Split(new Char[] { ',' });
string VNum = "";
int temp = -1;

Random rand = new Random();

for (int i = 1; i < VcodeNum + 1; i++)
{
if (temp != -1)
{
rand = new Random(i * temp * unchecked((int)DateTime.Now.Ticks));
}

int t = rand.Next(35);
if (temp != -1 && temp == t)
{
return RndNum(VcodeNum);
}
temp = t;
VNum += VcArray[t];
}
return VNum;
}

}

使用方法：
在需要它的页面html里添加

HttpCookieCollection cookies = Request.Cookies;
string tmp = cookies["ImageV"].Value;
然后比tmp与获取的较验证码文本框中的值是否相同

来源：网络