asp.net通过实现IHttpHandler接口方法给图片添加水印图片（动态添加，不破坏原图片，但是耗资源）

1. 添加一个类并实现IHttpHandler接口，类中需添加System.IO引用（类代码如下）

   using System;
   using System.Data;
   using System.Configuration;
   using System.Linq;
   using System.Web;
   using System.Web.Security;
   using System.Drawing;
   using System.IO;
   /// <summary>
   ///waterH 的摘要说明
   /// </summary>
   public class waterH:IHttpHandler
   {
       public waterH()
       {}
       private const string WATERMARK_URL = "~/Images/Watermark.png";
       private const string DEFAULTIMAGE_URL = "~/images/blank.gif";
       public void ProcessRequest(HttpContext context)
       {
           System.Drawing.Image Cover;
           if (File.Exists(context.Request.PhysicalPath))
           {
               Cover = Image.FromFile(context.Request.PhysicalPath);
               Image watermark = Image.FromFile(context.Request.MapPath(WATERMARK_URL));
               Graphics g = Graphics.FromImage(Cover);
               g.DrawImage(watermark, new Rectangle(Cover.Width - watermark.Width, Cover.Height - watermark.Height, watermark.Width, watermark.Height), 0, 0, watermark.Width, watermark.Height, GraphicsUnit.Pixel);
               g.Dispose();
               watermark.Dispose();
           }
           else
           {
               Cover = Image.FromFile(context.Request.MapPath(DEFAULTIMAGE_URL));
           }
           context.Response.ContentType = "images/jpeg";
           Cover.Save(context.Response.OutputStream, System.Drawing.Imaging.ImageFormat.Jpeg);
           Cover.Dispose();
           context.Response.End();
       }
   
       public bool IsReusable
       {
           get
           {
               return false;
           }
       }
   }

2. 配置web.config文件：
   在 <httpHandlers>节点中添加一下代码：
    <add verb="*" path="Images/*.jpg" type="waterH"/><!--path为图片放置路径，type为新添加的实现IHttpHandler接口的类名称-->
3. 配置ＩＩＳ：如图