wrapper for detecting multiple images

        Parameters:
        ----------
        im_list : list of str
            image path or list of image paths
        root_dir : str
            directory of input images, optional if image path already
            has full directory information
        extension : str
            image extension, eg. ".jpg", optional

        Returns:
        ----------
        list of detection results in format [det0, det1...], det is in
        format np.array([id, score, xmin, ymin, xmax, ymax]...)

def im_detect(self, im_list, root_dir=None, extension=None, show_timer=False):
        """
        wrapper for detecting multiple images

        Parameters:
        ----------
        im_list : list of str
            image path or list of image paths
        root_dir : str
            directory of input images, optional if image path already
            has full directory information
        extension : str
            image extension, eg. ".jpg", optional

        Returns:
        ----------
        list of detection results in format [det0, det1...], det is in
        format np.array([id, score, xmin, ymin, xmax, ymax]...)
        """
        test_db = TestDB(im_list, root_dir=root_dir, extension=extension)
        test_iter = DetIter(test_db, 1, self.data_shape, self.mean_pixels,
                            is_train=False)
        return self.detect_iter(test_iter, show_timer)