ASP.NETに透かしを付ける

using System;
using System.IO;
using System.Drawing;
using System.Drawing.Imaging;
using System.Data;
using System.Configuration;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;

using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;

/// <summary>
///ImageHandler      
/// </summary>
public class ImageHandler:IHttpHandler
{
    private const string waterMark_URL = "~/Images/waterMark.jpg";
    private const string defaultImage_URL = "~/Images/Default.jpg";

	public ImageHandler()
	{
		//
		//TODO:            
		//
	}

    public void ProcessRequest(HttpContext context)
    {
        System.Drawing.Image ImageConver;
        if (File.Exists(context.Request.PhysicalPath))
        {
            //    
            ImageConver = Image.FromFile(context.Request.PhysicalPath);
            //      
            Image waterMark = Image.FromFile(context.Request.MapPath(waterMark_URL));
            //    
            Graphics g = Graphics.FromImage(ImageConver);
            g.DrawImage(waterMark, new Rectangle(ImageConver.Width - waterMark.Width, ImageConver.Height - waterMark.Height, waterMark.Width, waterMark.Height), 0, 0, waterMark.Width, waterMark.Height, GraphicsUnit.Pixel);
            g.Dispose();
            waterMark.Dispose();
        }
        else
        {
            ImageConver=Image.FromFile(context.Request.MapPath(defaultImage_URL));
        }

        //      
        context.Response.ContentType="image/jpeg";
        ImageConver.Save(context.Response.OutputStream,System.Drawing.Imaging.ImageFormat.Jpeg);
        ImageConver.Dispose();
        context.Response.End();
    }

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