ASP.NET验证码如何实现

我主要是看到干扰线了，一个验证码里面要是没有干扰线什么的，至少得在噪点和随机码的排版上下工夫：

 /// <summary> /// 验证码生成类 /// </summary> public class verify_code : IHttpHandler, IRequiresSessionState {  public void ProcessRequest(HttpContext context)  {   int codeW = 80;   int codeH = 22;   int fontSize = 16;   string chkCode = string.Empty;   //颜色列表，用于验证码、噪线、噪点    Color[] color = { Color.Black, Color.Red, Color.Blue, Color.Green, Color.Orange, Color.Brown, Color.Brown, Color.DarkBlue };   //字体列表，用于验证码    string[] font = { "Times New Roman", "Verdana", "Arial", "Gungsuh", "Impact" };   //验证码的字符集，去掉了一些容易混淆的字符    char[] character = { '0', '1', '2', '3', '4', '5', '6', '8', '9' };   Random rnd = new Random();   //生成验证码字符串    for (int i = 0; i < 4; i++)   {    chkCode += character[rnd.Next(character.Length)];   }   //写入Session   context.Session["sys_verify_code"] = chkCode;   //创建画布   Bitmap bmp = new Bitmap(codeW, codeH);   Graphics g = Graphics.FromImage(bmp);   g.Clear(Color.White);   //画噪线    for (int i = 0; i < 4; i++)   {    int x1 = rnd.Next(codeW);    int y1 = rnd.Next(codeH);    int x2 = rnd.Next(codeW);    int y2 = rnd.Next(codeH);    Color clr = color[rnd.Next(color.Length)];    g.DrawLine(new Pen(clr), x1, y1, x2, y2);   }   //画验证码字符串    for (int i = 0; i < chkCode.Length; i++)   {    string fnt = font[rnd.Next(font.Length)];    Font ft = new Font(fnt, fontSize);    Color clr = color[rnd.Next(color.Length)];    g.DrawString(chkCode[i].ToString(), ft, new SolidBrush(clr), (float)i * 18 + 2, (float)0);   }   //画噪点    for (int i = 0; i < 100; i++)   {    int x = rnd.Next(bmp.Width);    int y = rnd.Next(bmp.Height);    Color clr = color[rnd.Next(color.Length)];    bmp.SetPixel(x, y, clr);   }   //清除该页输出缓存，设置该页无缓存    context.Response.Buffer = true;   context.Response.ExpiresAbsolute = System.DateTime.Now.AddMilliseconds(0);   context.Response.Expires = 0;   context.Response.CacheControl = "no-cache";   context.Response.AppendHeader("Pragma", "No-Cache");   //将验证码图片写入内存流，并将其以 "image/Png" 格式输出    MemoryStream ms = new MemoryStream();   try   {    bmp.Save(ms, ImageFormat.Png);    context.Response.ClearContent();    context.Response.ContentType = "image/Png";    context.Response.BinaryWrite(ms.ToArray());   }   finally   {    //显式释放资源     bmp.Dispose();    g.Dispose();   }  }  public bool IsReusable  {   get   {    return false;   }  } }

基本验证生成代码demo：

using System;using System.Drawing;using System.Drawing.Imaging;using System.IO;using System.Web;public partial class image : 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.White);  //文字字体  Font f = new Font("Arial Black", 10);  //文字颜色  SolidBrush s = new SolidBrush(Color.Black);  g.DrawString(VNum, f, s, 3, 3);  ms = new MemoryStream();  Img.Save(ms, ImageFormat.Jpeg);  Response.ClearContent();  Response.ContentType = "image/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; }}