VS2005.NET C# 编写验证码：

来自：http://zhidao.baidu.com/question/25377425.html

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;public partial class ValidateCode : System.Web.UI.Page{     protected void Page_Load(object sender, EventArgs e)     {         string checkCode = CreateRandomCode(4);         Session["CheckCode"] = checkCode;         CreateImage(checkCode);     }     private string CreateRandomCode(int codeCount)     {         string allChar = "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,W,X,Y,Z";         string[] allCharArray = allChar.Split(',');         string randomCode = "";         int temp = -1;         Random rand = new Random();         for (int i = 0; i < codeCount; i++)         {             if (temp != -1)             {                 rand = new Random(i * temp * ((int)DateTime.Now.Ticks));             }             int t = rand.Next(35);             if (temp == t)             {                 return CreateRandomCode(codeCount);             }             temp = t;             randomCode += allCharArray[t];         }         return randomCode;     }     private void CreateImage(string checkCode)     {         int iwidth = (int)(checkCode.Length * 11.5);         System.Drawing.Bitmap image = new System.Drawing.Bitmap(iwidth, 20);         System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(image);         System.Drawing.Font f = new System.Drawing.Font("Arial", 10, System.Drawing.FontStyle.Bold);         System.Drawing.Brush b = new System.Drawing.SolidBrush(System.Drawing.Color.White);         //g.FillRectangle(new System.Drawing.SolidBrush(Color.Blue),0,0,image.Width, image.Height);         g.Clear(System.Drawing.Color.Blue);         g.DrawString(checkCode, f, b, 3, 3);         System.Drawing.Pen blackPen = new System.Drawing.Pen(System.Drawing.Color.Black, 0);         Random rand = new Random();         for (int i = 0; i < 5; i++)         {             int y = rand.Next(image.Height);             g.DrawLine(blackPen, 0, y, image.Width, y);         }         System.IO.MemoryStream ms = new System.IO.MemoryStream();         image.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);         Response.ClearContent();         Response.ContentType = "image/Jpeg";         Response.BinaryWrite(ms.ToArray());         g.Dispose();         image.Dispose();     }}//g.FillRectangle(new System.Drawing.SolidBrush(Color.Blue),0,0,image.Width, image.Height);g.Clear(Color.Blue);这两种方法都可以改变生成图片的背景颜色下面那个for循环用来生成一些随机的水平线在需要用到验证码的页面添加一个<asp:Image>控件即可，但是要把ImageUrl指向生成验证码的页面