如何在phpexcel中添加图像？

Can anyone give me example coding of insert image in phpexcel

i try using this code but the excel file cannot open because format extension is not valid

$gdImage = imagecreatefromjpeg('images/officelogo.jpg');
// Add a drawing to the worksheetecho date('H:i:s') . " Add a drawing to the worksheet
";
$objDrawing = new PHPExcel_Worksheet_MemoryDrawing();
$objDrawing->setName('Sample image');$objDrawing->setDescription('Sample image');
$objDrawing->setImageResource($gdImage);
$objDrawing->setRenderingFunction(PHPExcel_Worksheet_MemoryDrawing::RENDERING_JPEG);
$objDrawing->setMimeType(PHPExcel_Worksheet_MemoryDrawing::MIMETYPE_DEFAULT);
$objDrawing->setHeight(150);
$objDrawing->setWorksheet($objPHPExcel->getActiveSheet());
$objDrawing->setCoordinates('A3');