class Upload_mod extends CI_Model{

  var $gallery_path;
  var $gallery_path_url;

  function index(){
    parent::__construct();
    $this->gallery_path = realpath(APPPATH . '../uploads');
    $this->gallery_path_url = base_url().'uploads/';
  }

  function do_upload() {
    $config = array(
      'allowed_types' => 'jpg|jpeg|gif|png',
      'upload_path'   => $this->gallery_path);

    $this->load->library('upload');
    $this->upload->initialize($config);
    $this->upload->do_upload();
    $image_data = $this->upload->data();
    print_r($image_data);

    if ( ! $this->upload->do_upload())
    {
      $error = array('error' => $this->upload->display_errors());
      gd_info();
      echo $error;
    }

    $config['source_image'] = $image_data['full_path'];
    $config['new_image'] = $this->gallery_path . '/thumbs';
    $config['maintain_ratio'] = TRUE;
    $config['width'] = 75;
    $config['height'] = 50;

    $this->load->library('image_lib');
    $this->image_lib->initialize($config);
    $this->image_lib->resize();

    if ( ! $this->image_lib->resize())
    {
      echo $this->image_lib->display_errors();
    }

  }
}

$this->load->library('image_lib');
$this->image_lib->initialize($config);
// $this->image_lib->resize(); Remove this call to resize()

if ( ! $this->image_lib->resize())
{
  echo $this->image_lib->display_errors();
}

$this->load->library('image_lib');
$this->image_lib->initialize($config);
$success = $this->image_lib->resize();

if ( ! $success)
{
  echo $this->image_lib->display_errors();
}