Guardar imagen en codeigniter

public function guardarImagen($object){

$directorio = IMG_PATH.'/'.$object->directorio.'/';

$nombre_imagen = $object->nombre_imagen;

$ext = $object->ext;

$field_name = $object->field_name;

$config['upload_path'] = $directorio;

$config['allowed_types'] = 'gif|jpg|png';

$config['max_size'] = '15000';

$config['encrypt_name'] = FALSE;

$config['overwrite'] = FALSE;

$config['file_name'] = $nombre_imagen.'.'.$ext;

$this->load->library('upload');

$this->upload->initialize($config);

$data = array();

if(!$this->upload->do_upload($field_name)){

$this->upload->display_errors();

}else{

$data = $this->upload->data();

}

return $data;

}