fail to load image in cezpdf codeigniter

[eluser]beben[/eluser]
this is my code in controller

Code:

function exportPDF()
{
    $this->load->library('cezpdf');
    $this->load->helper('pdf');
    $this->cezpdf->cezpdf('a4','portrait');
    $data['unit_kerja']= $this->admin_model->getUnitKerjaPDF();
    $titlecolumn = array(
                        'id_indeks' => 'Nomor Indeks',
                        'nama_unit' => 'Nama Unit Kerja'
    );
    $this->cezpdf->ezTable($data['unit_kerja'],$titlecolumn,'Master Unit Kerja');
    $image=base_url().'images/bps.png';
    $this->cezpdf->ezImage($image);
    $this->cezpdf->ezSetMargins(50,50,50,50);
    $this->cezpdf->addText(50,32,8,'Printed on ' . date('m/d/Y h:i:s a'). ' copyright cmail system BPS');
    $this->cezpdf->ezStream();
}

when i called the controller,, the data is show well,, but i can't load the image... thank you...