diff --git a/include/dependencies.inc.php b/include/dependencies.inc.php
new file mode 100644
index 0000000..fb262be
--- /dev/null
+++ b/include/dependencies.inc.php
@@ -0,0 +1,112 @@
+<?php
+if (!defined('PHPWG_ROOT_PATH'))
+{
+  die('Hacking attempt!');
+}
+
+/**
+ * Required third-party plugins for Bratonien Tools features.
+ * gdThumb is intentionally NOT a dependency: the public selection UI must work
+ * with Piwigo's native thumbnails and alternative thumbnail plugins/themes.
+ */
+function bratonien_tools_required_plugins()
+{
+  return array(
+    'BatchDownloader' => array(
+      'name' => 'Batch Downloader',
+      'pem_extension_id' => 616,
+      'required_for' => 'Fotoauswahl und Sammeldownloads',
+    ),
+  );
+}
+
+/**
+ * Ensures required plugins are present and active.
+ * Missing plugins are installed from Piwigo Extension Manager when automatic
+ * extension installation is enabled. Failures are reported but do not destroy
+ * unrelated Bratonien Tools functionality (for example watermarks).
+ */
+function bratonien_tools_ensure_dependencies(&$messages = array())
+{
+  global $conf;
+
+  if (!defined('PHPWG_PLUGINS_PATH'))
+  {
+    $messages[] = 'Plugin-Abhängigkeiten konnten nicht geprüft werden: Piwigo-Pluginpfad fehlt.';
+    return false;
+  }
+
+  include_once(PHPWG_ROOT_PATH.'admin/include/plugins.class.php');
+  $plugins = new plugins();
+  $all_ok = true;
+
+  foreach (bratonien_tools_required_plugins() as $plugin_id => $dependency)
+  {
+    // Plugin files missing: try to retrieve the compatible PEM revision.
+    if (!isset($plugins->fs_plugins[$plugin_id]))
+    {
+      if (empty($conf['enable_extensions_install']))
+      {
+        $messages[] = $dependency['name'].' fehlt und die automatische Plugin-Installation ist in Piwigo deaktiviert.';
+        $all_ok = false;
+        continue;
+      }
+
+      if (!$plugins->get_server_plugins(true) || empty($plugins->server_plugins[$dependency['pem_extension_id']]))
+      {
+        $messages[] = $dependency['name'].' fehlt und konnte im Piwigo Extension Manager nicht gefunden werden.';
+        $all_ok = false;
+        continue;
+      }
+
+      $remote = $plugins->server_plugins[$dependency['pem_extension_id']];
+      if (empty($remote['revision_id']))
+      {
+        $messages[] = $dependency['name'].' fehlt; der Extension Manager lieferte keine installierbare Revision.';
+        $all_ok = false;
+        continue;
+      }
+
+      $installed_id = null;
+      $status = $plugins->extract_plugin_files('install', $remote['revision_id'], $dependency['pem_extension_id'], $installed_id);
+      if ($status !== 'ok')
+      {
+        $messages[] = $dependency['name'].' konnte nicht automatisch installiert werden ('.$status.').';
+        $all_ok = false;
+        continue;
+      }
+
+      // Refresh the plugin inventory after extraction. The folder ID is the
+      // authoritative runtime identifier, not the PEM extension number.
+      $plugins = new plugins();
+      if (!isset($plugins->fs_plugins[$plugin_id]))
+      {
+        $messages[] = $dependency['name'].' wurde geladen, aber nicht unter dem erwarteten Plugin-ID "'.$plugin_id.'" gefunden.';
+        $all_ok = false;
+        continue;
+      }
+
+      $messages[] = $dependency['name'].' wurde automatisch installiert.';
+    }
+
+    $state = isset($plugins->db_plugins_by_id[$plugin_id])
+      ? $plugins->db_plugins_by_id[$plugin_id]['state']
+      : 'uninstalled';
+
+    if ($state !== 'active')
+    {
+      $errors = $plugins->perform_action('activate', $plugin_id);
+      if (!empty($errors))
+      {
+        $messages[] = $dependency['name'].' konnte nicht aktiviert werden: '.implode(' ', (array)$errors);
+        $all_ok = false;
+        continue;
+      }
+
+      $messages[] = $dependency['name'].' wurde automatisch aktiviert.';
+      $plugins = new plugins();
+    }
+  }
+
+  return $all_ok;
+}