diff --git a/css/003-gallery.css b/css/003-gallery.css
index f3343c9..a0d26ca 100644
--- a/css/003-gallery.css
+++ b/css/003-gallery.css
@@ -7,7 +7,6 @@
         display: flex;
         flex-direction: row;
         align-items: center;
-        justify-content: center;
         position: fixed;
         bottom: 0;
         width: 100%;
diff --git a/module.php b/module.php
index 724908c..6b0896e 100644
--- a/module.php
+++ b/module.php
@@ -10,7 +10,10 @@ return new class extends Lewp\Module
     const KEY_START_LANDSCAPE_ID = "start_landscape_id";
     const KEY_START_PORTRAIT_ID = "start_portrait_id";
     const KEY_START_MODULE_ID = "start_module_id";
-    const KEY_GALLERY_FOLDER_ID = "gallery_folder_id";
+    const KEY_GALLERY_LANDSCAPE_FOLDER_ID = "gallery_landscape_folder_id";
+    const KEY_GALLERY_PORTRAIT_FOLDER_ID = "gallery_portrait_folder_id";
+    const KEY_GALLERY_IMAGE_EXTENSION = "image_extension";
+    const KEY_ORIENTATION_PRIORITY = "orientation_priority";
 
     private function createBigImageContainer()
     {
@@ -50,12 +53,23 @@ return new class extends Lewp\Module
     private function galleryAvailable(array $options) : bool
     {
         $retval = true;
-        if (!isset($options[self::KEY_GALLERY_FOLDER_ID])) {
+        if (!isset($options[self::KEY_GALLERY_LANDSCAPE_FOLDER_ID])) {
+            $retval = false;
+        }
+        if (!isset($options[self::KEY_GALLERY_PORTRAIT_FOLDER_ID])) {
             $retval = false;
         }
         return $retval;
     }
 
+    private function generateGalleryPath(string $base_path, string $folder_id) : string
+    {
+        return Resolve::toFilepath([
+            $base_path,
+            Resolve::idToFilepathRel($folder_id)
+        ]);
+    }
+
     private function createGallery(array $options)
     {
         $div = $this->createAndSetupElement(
@@ -67,51 +81,56 @@ return new class extends Lewp\Module
         );
 
         // get all filenames
-        $folderpaths = $this->findFolderPaths('res-images');
-        for ($i = 0; $i < sizeof($folderpaths); ++$i) {
-            if ($folderpaths[$i] === false) {
-                continue;
-            }
-            // folder path of gallery
-            $gallery_folder = Resolve::toFilepath([
-                $folderpaths[$i],
-                $options[self::KEY_GALLERY_FOLDER_ID]
-            ]);
-            // all images in the folder
-            $gallery_filenames = scandir($gallery_folder);
-            // check if folder is empty or not available
-            if (
-                ($gallery_filenames === false)
-                || (sizeof($gallery_filenames) == 2)
-            ) {
-                continue;
-            }
-            foreach ($gallery_filenames as $image) {
-                if ($image === '..' || $image === '.') {
-                    continue;
-                }
-                $landscape =
-                    $options[self::KEY_GALLERY_FOLDER_ID]
-                    .Resolve::ID_SEPARATOR
-                    .$image;
-                $rwd = new RwdPicture(
-                    $landscape,
-                    $landscape,
-                    $this->getModuleId()
-                );
-                $div->appendChild(
-                    $this->importNode($rwd->getPictureTag(), true)
-                );
-            }
-            break; // the loop should only run one time to the end
+        $fileids_first = $this->collectResourceFileIds(
+            'res-images',
+            $options[self::KEY_GALLERY_LANDSCAPE_FOLDER_ID],
+            '*.'.$options[self::KEY_GALLERY_IMAGE_EXTENSION]
+        );
+        $tmp = $this->collectResourceFileIds(
+            'res-images',
+            $options[self::KEY_GALLERY_PORTRAIT_FOLDER_ID],
+            '*.'.$options[self::KEY_GALLERY_IMAGE_EXTENSION]
+        );
+        if ($options[self::KEY_ORIENTATION_PRIORITY] === 'portrait') {
+            $fileids_second = $fileids_first;
+            $fileids_first = $tmp;
+        } else {
+            $fileids_second = $tmp;
         }
 
+        foreach ($fileids_first as $image) {
+            $landscape = Resolve::arrayToId([
+                $options[self::KEY_GALLERY_LANDSCAPE_FOLDER_ID],
+                $image
+            ]);
+            $portrait = $landscape;
+            // check if the portrait file is available
+            if (in_array($image, $fileids_second)) {
+                $portrait = Resolve::arrayToId([
+                $options[self::KEY_GALLERY_PORTRAIT_FOLDER_ID],
+                $image
+            ]);;
+            }
+            $rwd = new RwdPicture(
+                $landscape,
+                $portrait,
+                $this->getModuleId()
+            );
+            $div->appendChild(
+                $this->importNode($rwd->getPictureTag(), true)
+            );
+        }
         return $div;
-
     }
 
     public function run(array $options = []) : bool
     {
+        // add default options
+        $options += [
+            self::KEY_ORIENTATION_PRIORITY => 'landscape',
+            self::KEY_GALLERY_IMAGE_EXTENSION => 'jpg'
+        ];
+
         $big_image_container = $this->createBigImageContainer();
         if ($this->bigImageAvailable($options)) {
             $big_image = $this->createBigImage(