public class PictureHttpHandler : IHttpHandler
{
    public bool IsReusable
    {
        get { return true; }
    }

    public void ProcessRequest(HttpContext context)
    {
        //站點(diǎn)的域名
        string myDomain = "localhost";

        if (context.Request.UrlReferrer == null ||
            context.Request.UrlReferrer.Host.ToLower().IndexOf(myDomain) < 0)
        {
            //如果是通過瀏覽器直接訪問或者是通過其他站點(diǎn)訪問過來的，則顯示“資源不存在”圖片
            context.Response.ContentType = "image/JPEG";
            context.Response.WriteFile(context.Request.PhysicalApplicationPath + "/images/noimg.jpg");
        }
        else
        {
            //如果是通過站內(nèi)訪問的，這正常顯示圖片
            context.Response.ContentType = "image/JPEG";
            context.Response.WriteFile(context.Request.PhysicalPath);
        }

    }
}

<httpHandlers>
      <!--path中指定的是執(zhí)行type中HttpHandler的訪問路徑。此路徑可以帶后綴也可以不帶后綴。如果path配置為*，則會(huì)對(duì)所有的請(qǐng)求執(zhí)行此HttpHandler-->
     <add  verb="*" path="*.jpg" type="MyHttpHandler.PictureHttpHandler,MyHttpHandler"/>
</httpHandlers>

public class ValidateCodeHttpHandler : IHttpHandler
{
    public void ProcessRequest(HttpContext context)
    {
        context.Response.ContentType = "image/gif";
        //建立Bitmap對(duì)象，繪圖        
        Bitmap basemap = new Bitmap(200, 60);
        Graphics graph = Graphics.FromImage(basemap);
        graph.FillRectangle(new SolidBrush(Color.White), 0, 0, 200, 60);
        Font font = new Font(FontFamily.GenericSerif, 48, FontStyle.Bold, GraphicsUnit.Pixel);
        Random r = new Random();
        string letters = "ABCDEFGHIJKLMNPQRSTUVWXYZ";
        string letter;
        StringBuilder s = new StringBuilder();
        //添加隨機(jī)的五個(gè)字母        
        for (int x = 0; x < 5; x++)
        {
            letter = letters.Substring(r.Next(0, letters.Length - 1), 1);
            s.Append(letter);
            graph.DrawString(letter, font, new SolidBrush(Color.Black), x * 38, r.Next(0, 15));
        }
        //混淆背景        
        Pen linePen = new Pen(new SolidBrush(Color.Black), 2);
        for (int x = 0; x < 6; x++)
            graph.DrawLine(linePen, new Point(r.Next(0, 199), r.Next(0, 59)),
                new Point(r.Next(0, 199), r.Next(0, 59)));
        //將圖片保存到輸出流中              
        basemap.Save(context.Response.OutputStream, ImageFormat.Gif);
        //context.Session["CheckCode"] = s.ToString();   
        //如果沒有實(shí)現(xiàn)IRequiresSessionState，則這里會(huì)出錯(cuò)，也無法生成圖片         
        context.Response.End();
    }
    public bool IsReusable
    {
        get { return true; }
    }
}

<add  verb="*" path="validatevode" type="MyHttpHandler.ValidateCodeHttpHandler,MyHttpHandler"/>

public class ModuleExample : IHttpModule
{
    public void Init(System.Web.HttpApplication application)
    {
        application.PostAuthenticateRequest += (sender, args) =>
         {
             HttpContext context = ((HttpApplication)sender).Context;
             context.Response.Write("請(qǐng)求PostAuthenticate");
         };

        application.BeginRequest += (sender, args) =>
        {
            HttpContext context = ((HttpApplication)sender).Context;
            context.Response.Write("請(qǐng)求到達(dá)");
        };

        application.EndRequest += (sender, args) =>
        {
            HttpContext context = ((HttpApplication)sender).Context;
            context.Response.Write("請(qǐng)求結(jié)束");
        };
    }
    public void Dispose()
    {
        throw new NotImplementedException();
    }
}

<system.webServer>
    <modules>
    　　<add name="ModuleExample" type="Samples.ModeleExample">
    </modules>
</system.webServer>

<httpModules>
    <add name="OutputCache" type="System.Web.Caching.OutputCacheModule" />
    <add name="Session" type="System.Web.SessionState.SessionStateModule" />
    <add name="WindowsAuthentication" type="System.Web.Security.WindowsAuthenticationModule" />
    <add name="FormsAuthentication" type="System.Web.Security.FormsAuthenticationModule" />
    <add name="PassportAuthentication" type="System.Web.Security.PassportAuthenticationModule" />
    <add name="RoleManager" type="System.Web.Security.RoleManagerModule" />
     <add name="UrlAuthorization" type="System.Web.Security.UrlAuthorizationModule" />
     <add name="FileAuthorization" type="System.Web.Security.FileAuthorizationModule" />
     <add name="AnonymousIdentification" type="System.Web.Security.AnonymousIdentificationModule" />
     <add name="Profile" type="System.Web.Profile.ProfileModule" />
     <add name="ErrorHandlerModule" type="System.Web.Mobile.ErrorHandlerModule, System.Web.Mobile, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" />
     <add name="ServiceModel" type="System.ServiceModel.Activation.HttpModule, System.ServiceModel.Activation, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" />
     <add name="UrlRoutingModule-4.0" type="System.Web.Routing.UrlRoutingModule" />
     <add name="ScriptModule-4.0" type="System.Web.Handlers.ScriptModule, System.Web.Extensions, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>
 </httpModules>