登陆框中用到的验证码

在登陆框中，用一个图片控件：

　　　　　　　　　　<div id="CheckDiv" runat="server">
                    <label>验证码：</label>
                    <asp:TextBox ID="tbCode" runat="server"/>
                    <img id="imgCode" src="CheckCode.aspx" alt="看不清？" onclick="javascript:GetCheckCode()"/>
                 </div>

GetCheckCode是JS事件，用来手动刷新验证码：

function GetCheckCode() {
    document.getElementById("imgCode").src = "CheckCode.aspx";
}

最好，来到重要的验证码生成页面。由上面的引用已经可以看到，CheckCode.aspx是一个页面，而且这个页面的主要职责就是输出一个位图图象。PS.这个页面的前端代码没有任何额外的，就是新建时的默认。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Drawing;

namespace KeySystem
{
    public partial class CheckCode : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            CreateCheckCodeImage(GenerateCheckCode());// 页面加载时调用方法绘制验证码
        }

        private string GenerateCheckCode()
        {
            int number;
            char code;
            string checkCode = string.Empty;
            Random random = new Random();
            for (int i = 0; i < 4; i++)
            {
                number = random.Next();
                code =(char)('0'+(char)(number % 10));
                checkCode += code.ToString();
            }
            Response.Cookies.Add(new HttpCookie("CheckCode", checkCode));
            return checkCode;
        }

        private void CreateCheckCodeImage(string checkCode)
        {
            if (checkCode == null || checkCode.Trim() == String.Empty)
                return;
            //开始创建一个位图
            System.Drawing.Bitmap image = new System.Drawing.Bitmap((int)Math.Ceiling(checkCode.Length * 12.5), 22);
            Graphics g = Graphics.FromImage(image);
          
            try
            {
                Random random = new Random();
                g.Clear(Color.White);
                for (int i = 0; i < 2; i++)//图片背景噪音线
                {
                    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 Pen(Color.Black), x1, y1, x2, y2);
                }

                Font font = new System.Drawing.Font("Arial", 12, System.Drawing.FontStyle.Bold);

                System.Drawing.Drawing2D.LinearGradientBrush brush =
                    new System.Drawing.Drawing2D.LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height),
                        Color.Blue, Color.DarkRed, 1.2f, true);

                g.DrawString(checkCode,font,Brushes.Black,2,2);//绘制文字

                //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, Color.FromArgb(random.Next()));
                }

                //图片的边框线
                g.DrawRectangle(new Pen(Color.Silver), 0, 0, image.Width - 1, image.Height - 1);

                //输出
                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();
            }
        }
    }
}