asp.net动态添加图片水印

<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>

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.Width - watermark.Width);
int height = r.Next(10,Cover.Height - watermark.Height);
g.DrawImage(watermark, new Rectangle(width, 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 = "image/Jpeg";
Cover.Save(context.Response.OutputStream, System.Drawing.Imaging.ImageFormat.Jpeg);
Cover.Dispose();
context.Response.End();

}
public bool IsReusable
{
get
{
return false;
}
}

#endregion
}