asp.net动态添加图片水印

web.config
<httpHandlers>
<remove verb="*" path="*.asmx"/>
<add verb="*" path="*.asmx" validate="false" type="System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>
<add verb="*" path="*_AppService.axd" validate="false" type="System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>
<add verb="GET,HEAD" path="ScriptResource.axd" type="System.Web.Handlers.ScriptResourceHandler, System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" validate="false"/>
<add verb="*" path="images/shangjia/*/*.jpg" type="CoverHandler"/>
<add verb="*" path="images/shangjia/*/*/*.jpg" type="CoverHandler"/>
<add verb="*" path="admin/TotalUpImg/VedioImg/*.jpg" type="CoverHandler1"/>
</httpHandlers>
CoverHandler.cs
using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.IO;
using System.Drawing;
using System.Drawing.Imaging;
/// <summary>
/// CoverHandler 的摘要说明
/// </summary>
public class CoverHandler : IHttpHandler
{
public CoverHandler()
{
//
// TODO: 在此处添加构造函数逻辑
//
}
private const string WATERMARK_URL = "~/images/WaterMark.png";
private const string DEFAULTIMAGE_URL = "~/images/default.jpg";
#region IHttpHandler 成员
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);
Random r = new Random();
int width = r.Next(10,Cover.