$fpdf->Image('https://chart.googleapis.com/chart?chs=150x150&cht=qr&chl=SoyUnDios&.png',100,100,10);
<?phprequire_once("fpdf.php"); $pdf = new FPDF();$pdf->AddPage();$pdf->SetFont('Arial','B',16);$pdf->Cell(40,10,'Esto es un codigo QR xD');$pdf->Image('http://chart.googleapis.com/chart?chs=100x100&cht=qr&chl=SoyUnDios&.png',20,20,100,100);$pdf->Output();?>