Lập Trình .NET

public static void AddWatermarkUsingHeaderFooterImage(OfficeOpenXml.ExcelWorksheet worksheet, System.Drawing.Image image)
{
 //Enable PageLayoutView mode to see the watermark
 worksheet.View.PageLayoutView = true;
 worksheet.HeaderFooter.EvenHeader.InsertPicture(image, PictureAlignment.Centered);
 worksheet.HeaderFooter.OddHeader.InsertPicture(image, PictureAlignment.Centered);
}

public static void AddWatermarkUsingBackgroundImage(OfficeOpenXml.ExcelWorksheet worksheet, System.Drawing.Image image)
{
  worksheet.BackgroundImage.Image = image;
}