asp.net生成缩略图及给原始图加水印

using System.IO;
using System.Drawing.Imaging;
  private void Button1_ServerClick(object sender, System.EventArgs e)
  {
    Graphics g=null;
    System.Drawing.Image upimage=null; 
    System.Drawing.Image thumimg=null; 
    System.Drawing.Image simage=null;
    Bitmap outputfile=null;
    try
    {
      string extension = Path.GetExtension(File1.PostedFile.FileName).ToUpper();
      string filename = DateTime.Now.ToString("yyyyMMddhhmmss");
      string smallpath = Server.MapPath(".")+"/smallimg/";
      string bigpath = Server.MapPath(".")+"/bigimg/";
      int width,height,newwidth,newheight;
      System.Drawing.Image.GetThumbnailImageAbort callb =new System.Drawing.Image.GetThumbnailImageAbort(ThumbnailCallback);    
    if(!Directory.Exists(smallpath))
     Directory.CreateDirectory(smallpath);
    if(!Directory.Exists(bigpath))
     Directory.CreateDirectory(bigpath);
    Stream upimgfile = File1.PostedFile.InputStream;
    string simagefile = Server.MapPath("a8logo.jpg"); //要加水印的文件
    simage=System.Drawing.Image.FromFile(simagefile);
    upimage= System.Drawing.Image.FromStream(upimgfile); //上传的图片
    width = upimage.Width;
    height = upimage.Height;
    if(width>height)
    {
     newwidth=200;
     newheight =(int)((double)height/(double)width * (double)newwidth);
    }
    else
    { 
     newheight=200;
     newwidth=(int)((double)width/(double)height * (double)newheight);   
    }   
    thumimg = upimage.GetThumbnailImage(newwidth,newheight,callb,IntPtr.Zero); 
    outputfile=new Bitmap(upimage);
    g=Graphics.FromImage(outputfile);
    g.DrawImage(simage,new Rectangle(upimage.Width-simage.Width,upimage.Height-simage.Height,upimage.Width,upimage.Height),0,0,upimage.Width,upimage.Height,GraphicsUnit.Pixel);
    
    string newpath = bigpath + filename + extension;     //原始图路径
    string thumpath = smallpath + filename + extension;  //缩略图路径
    outputfile.Save(newpath);
    thumimg.Save(thumpath);
    outputfile.Dispose();
    
   }
   catch(Exception ex)
   {
    throw ex;
   }
   finally
   {
    if(g!=null)
     g.Dispose();
    if(thumimg!=null)
     thumimg.Dispose();
    if(upimage!=null)
     upimage.Dispose();
    if(simage!=null)
     simage.Dispose();
   }
  }
  public bool ThumbnailCallback()
  {
   return false;
  }