จากตัวอย่างที่มีให้ศึกษาเรื่องการ upload รูป และใส่ WaterMark ผมติดปัญหาอ่าครับ

	void ddlNum_Changed(object sender, System.EventArgs e)
	{
	    int i = 0;
	    FileUpload fileUpload;
	    Label lblBr;
	    for (i = 1; i <= Convert.ToInt32(this.ddlNum.SelectedItem.Value); i++) {
	        fileUpload = new FileUpload();
	        {
	            fileUpload.ID = "fiUpload" + i;
	        }
	        lblBr = new Label();
	        lblBr.Text = "<br>";
	        this.pnlCtrl.Controls.Add(fileUpload);
	        this.pnlCtrl.Controls.Add(lblBr);
	    }
	    
	    if (Convert.ToInt32(this.ddlNum.SelectedItem.Value) > 0) {
	        this.pnlUpload.Visible = true;
	    }
	    else {
	        this.pnlUpload.Visible = false;
	        this.form1.Enctype = "multipart/form-data";
	    }
	}

	void btnUpload_OnClick(object sender, EventArgs e)
	{
	
	    int i = 0;
	    HttpFileCollection myUpoad = Request.Files;
	    HttpPostedFile myFiles;
	    string FileName = null;
	    string NewFileName = null;
	    for (i = 0; i <= Convert.ToInt32(this.ddlNum.SelectedItem.Value) - 1; i++) {
	        myFiles = myUpoad[i];
	        //*** Check Control ***//
	        if (myUpoad.Keys[i].ToString() == ("fiUpload" + (i + 1)).ToString()) {
	            if (!string.IsNullOrEmpty((myFiles.FileName))) {
	                FileName = "MyUpload/" + System.IO.Path.GetFileName(myFiles.FileName);
	                NewFileName = "MyUpload/Thumbnail_" + System.IO.Path.GetFileName(myFiles.FileName);
	                
	                //*** Upload Original Images ***//
	                myFiles.SaveAs(Server.MapPath(FileName));	                
	                //*** Call to function resize ***//                  
                    WriteWaterMark(FileName);
	                ResizeImages(FileName, NewFileName);
	                
	                this.lblText.Text = this.lblText.Text + System.IO.Path.GetFileName(myFiles.FileName) + " uploaded & resize.<br>";
	            }
	            
	        }
	    }
	    this.ddlNum.Visible = false;
	    this.pnlUpload.Visible = false;
	}

	void ResizeImages(object FileName, object NewFileName)
	{
	    int intWidth = 0;
	    int intHeight = 0;
	    
	    intWidth = 130;
	    //*** Fix Width ***//
	    intHeight = 100;
	    //*** If = 0 Auto Re-Cal Size ***//
	    
	    System.Drawing.Image objGraphic = System.Drawing.Image.FromFile(Server.MapPath(FileName.ToString()));
	    
	    Bitmap objBitmap;
	    //*** Calculate Height ***//
	    if (intHeight > 0) {
	        objBitmap = new Bitmap(objGraphic, intWidth, intHeight);
	    }
	    else {
	        if (objGraphic.Width > intWidth) {
	            double ratio = objGraphic.Height / objGraphic.Width;
	            intHeight = (int)ratio * (int)intWidth;
	            objBitmap = new Bitmap(objGraphic, intWidth, intHeight);
	        }
	        else {
	            objBitmap = new Bitmap(objGraphic);
	        }
	    }
	    
	    //*** Save As  ***//
	    objBitmap.Save(Server.MapPath(NewFileName.ToString()), objGraphic.RawFormat);
	    
	    //*** Close ***//
	    objGraphic.Dispose();
	    
	    //*** Nothing ***//
	    objBitmap = null;
	    objGraphic = null;
	    
	}
    
    
    
    void WriteWaterMark(object FileName)
    {
      

            Bitmap objBitmap = new System.Drawing.Bitmap(Server.MapPath(FileName.ToString()));
            Graphics objGraphic = Graphics.FromImage(objBitmap);
            //*** Write Text ***//
            string strText = "CopyRight 2009 (www.ThaiCreate.Com)";
            //*** String ***//
            Font objFont = new Font("Tahoma", 10);
            //*** Font Style ***//
            SolidBrush objBrushWrite = new SolidBrush(Color.Red);
            //*** Font Color ***//

            //*** Text Align ***//
            StringFormat strFormat = new StringFormat();
            strFormat.Alignment = StringAlignment.Far;
            //*** .Near (Left) , .Far (Right) ***// 
            strFormat.LineAlignment = StringAlignment.Far;
            //*** .Near (Top) , .Far (Down) ***// 

            //*** DrawString ***//
            objGraphic.DrawString(strText, objFont, objBrushWrite, new Rectangle(0, 0, objBitmap.Width, objBitmap.Height), strFormat);

            //*** Save As ***//
            objBitmap.Save(Server.MapPath(FileName.ToString()), ImageFormat.Jpeg);   ******* ฟ้อง error ตรงนี้ครับ *******

            //*** Close ***//
            objGraphic.Dispose();

            //*** Nothing ***//
            objBitmap = null;
            objGraphic = null;

        }