public class Picture : PositionedElement 

using( var workbook = Workbook.Create( "test.xlsx") )
  {
    // Get the first worksheet. A workbook contains at least 1 worksheet.
    var worksheet = workbook.Worksheets[ 0 ];

    var stream = new FileStream( PictureSampleResourcesDirectory + @"balloon.jpg", FileMode.Open, FileAccess.Read );
    // Add the stream picture in cell A4 and extend it to cell E12.
    var filenamePicture = worksheet.Pictures.Add( stream, "A4", "E12" );

    // Add the filename picture with its top left corner in 15th row and 1st column.
    var streamPicture = worksheet.Pictures.Add( PictureSampleResourcesDirectory + @"balloon.jpg", 14, 0 );

    workbook.Save();
  }