<%@ WebHandler Language="C#" Class="Handler" %>

using System;
using System.Data;
using System.Web;
using System.Drawing;
using System.Web.Services;
using System.Web.Services.Protocols;
using System.Collections;

public class Handler : IHttpHandler {
    
    public void ProcessRequest (HttpContext context) {
        //context.Response.ContentType = "text/plain";
        //context.Response.Write("Hello World");
        context.Response.Cache.SetCacheability(HttpCacheability.NoCache);//特别注意，如不加，单击验证图片＇看不清换一张＇，无效果．            
        this.CreateCheckCodeImage(GenerateCheckCode(context), context);
    }
 
    public bool IsReusable {
        get {
            return false;
        }
    }
    private string GenerateCheckCode(HttpContext context)
    {
        int number;  string checkCode = String.Empty;

        System.Random random = new Random();

        for (int i = 0; i < 4; i++)
        {
            number = random.Next(10);

            //if (number % 2 == 0)
            //    code = (char)('0' + (char)(number % 10));
            //else if (number % 3 == 0)
            //    code = (char)('A' + (char)(number % 26));
            //else
            //    code = (char)('a' + (char)(number % 26));
            checkCode += number.ToString();
        }
        context.Response.Cookies.Add(new HttpCookie("CheckCode", checkCode)); //也可以存到Seesion里．             //context.Session["CheckCode"] = checkCode;                        
        return checkCode;
    }
    private void CreateCheckCodeImage(string checkCode, HttpContext context)
    {
        if (checkCode == null || checkCode.Trim() == String.Empty) return;

        System.Drawing.Bitmap image = new System.Drawing.Bitmap((int)Math.Ceiling((checkCode.Length * 12.5)), 22); Graphics g = Graphics.FromImage(image);

        try
        {
            //生成随机生成器                
            Random random = new Random();

            //清空图片背景色                
            g.Clear(Color.White);

            //画图片的背景噪音线                
            for (int i = 0; i < 10; 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 Pen(Color.Silver), x1, y1, x2, y2);
            }

            Font font = new System.Drawing.Font("Arial", 12, (System.Drawing.FontStyle.Bold | System.Drawing.FontStyle.Italic));
            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, brush, 2, 2);

            //画图片的前景噪音点                
            for (int i = 0; i < 20; i++)
            {
                int x = random.Next(image.Width); int y = random.Next(image.Height);

                image.SetPixel(x, y, Color.FromArgb(random.Next()));
            }

            //画图片的边框线                
            g.DrawRectangle(new Pen(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);
            context.Response.ClearContent(); context.Response.ContentType = "image/Gif"; context.Response.BinaryWrite(ms.ToArray());
        }
        finally
        {
            g.Dispose();
            image.Dispose();
        }

    }
}