asp.net验证码

<%@ Page Language="C#" Debug="true" %>

<%
int number;
   char code;
   string checkCode = String.Empty;

   System.Random random = new Random();

   for(int i=0; i<4; i++)
   {
    number = random.Next();

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

    checkCode += code.ToString();
    }
if(checkCode == null || checkCode.Trim() == String.Empty)
    return;
Session.Add("vCode", checkCode);
   System.Drawing.Bitmap image = new System.Drawing.Bitmap((int)Math.Ceiling((checkCode.Length * 12.5)), 22);
   System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(image);

   try
   {
    //生成随机生成器

    //清空图片背景色
    g.Clear(System.Drawing.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 System.Drawing.Pen(System.Drawing.Color.Silver), x1, y1, x2, y2);
    }

    System.Drawing.Font font = new System.Drawing.Font("Arial", 12, (System.Drawing.FontStyle.Bold ));
    System.Drawing.Drawing2D.LinearGradientBrush brush = new System.Drawing.Drawing2D.LinearGradientBrush(new System.Drawing.Rectangle(0, 0, image.Width, image.Height), System.Drawing.Color.Blue, System.Drawing.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, System.Drawing.Color.FromArgb(random.Next()));
    }

    //画图片的边框线
    g.DrawRectangle(new System.Drawing.Pen(System.Drawing.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();
   }
%>

 

登录页面调用<img src="验证码页面"/>

点击图片切换验证码

<img id="checkImg" src="checkImg.aspx" onclick="this.src=this.src+'?'" />

点击换一张连接电泳js

function changeImage()
    {
        var s = document.getElementById("checkImg").src;
        document.getElementById("checkImg").src=s+"?";
    }