function custom_gallery_shortcode($atts) {
    $atts = shortcode_atts(array(
        'folder' => 'test.cam.01',  // デフォルトのフォルダー名
    ), $atts);

    $folder_path = WP_CONTENT_DIR . '/camera_data/' . $atts['folder'];
    $images = scandir($folder_path, SCANDIR_SORT_DESCENDING);
    $image_html = '';

    foreach ($images as $image) {
        if ($image !== '.' && $image !== '..') {
            $image_url = content_url('camera_data/' . $atts['folder'] . '/' . $image);
            $image_html .= '<img src="' . $image_url . '" alt="' . $image . '">';
        }
    }

    return $image_html;
}
add_shortcode('custom_gallery', 'custom_gallery_shortcode');