diff --git a/backend/__pycache__/app.cpython-312.pyc b/backend/__pycache__/app.cpython-312.pyc
index 13b0fe0..2532eb2 100644
Binary files a/backend/__pycache__/app.cpython-312.pyc and b/backend/__pycache__/app.cpython-312.pyc differ
diff --git a/backend/app.py b/backend/app.py
index dfa7081..5f6a708 100644
--- a/backend/app.py
+++ b/backend/app.py
@@ -7,10 +7,12 @@ from pathlib import Path
 from urllib.parse import urlencode
 from zoneinfo import ZoneInfo, ZoneInfoNotFoundError
 
+from PIL import Image, ImageOps, UnidentifiedImageError
 from flask import (
     Flask,
     flash,
     g,
+    jsonify,
     redirect,
     render_template,
     request,
@@ -27,6 +29,10 @@ base_dir = Path(__file__).resolve().parent
 app.config["SECRET_KEY"] = os.environ.get("SECRET_KEY", "change-me-in-production")
 app.config["DB_PATH"] = os.environ.get("DB_PATH", str(base_dir / "app.sqlite3"))
 app.config["UPLOAD_FOLDER"] = os.environ.get("UPLOAD_FOLDER", str(base_dir / "uploads"))
+app.config["THUMBNAIL_FOLDER"] = os.environ.get(
+    "THUMBNAIL_FOLDER",
+    str(Path(app.config["UPLOAD_FOLDER"]) / "thumbnails"),
+)
 app.config["MAX_CONTENT_LENGTH"] = int(os.environ.get("MAX_UPLOAD_BYTES", str(64 * 1024 * 1024)))
 app.config["LOCATION_NAME"] = os.environ.get("LOCATION_NAME", "Hochheimer Terrasse")
 app.config["LOCATION_ADDRESS"] = os.environ.get("LOCATION_ADDRESS", "Mainzer Str. 22, 65239 Hochheim am Main")
@@ -41,16 +47,19 @@ app.config["WEDDING_COUNTDOWN_LOCAL"] = os.environ.get("WEDDING_COUNTDOWN_LOCAL"
 app.config["WEDDING_TIMEZONE"] = os.environ.get("WEDDING_TIMEZONE", "Europe/Berlin")
 app.config["HERO_IMAGE_FILENAME"] = os.environ.get("HERO_IMAGE_FILENAME")
 
-ALLOWED_EXTENSIONS = {"jpg", "jpeg", "png", "heic", "heif"}
+ALLOWED_EXTENSIONS = {"jpg", "jpeg", "png", "gif", "heic", "heif"}
 ALLOWED_MIME_TYPES = {
     "image/jpeg",
     "image/jpg",
     "image/png",
+    "image/gif",
     "image/heic",
     "image/heif",
     "image/heic-sequence",
     "image/heif-sequence",
 }
+THUMBNAIL_EXTENSIONS = {"jpg", "jpeg", "png"}
+THUMBNAIL_MAX_SIZE = (900, 900)
 
 LOCATION_VIDEO_EXTENSIONS = {".mp4", ".webm", ".mov", ".m4v"}
 ONBOARDING_VERSION = 2
@@ -322,7 +331,11 @@ TEXTS = {
         "upload_multi_hint": "Du kannst mehrere Bilder auf einmal auswählen oder weitere Felder hinzufügen.",
         "upload_selected_count": "{count} Bilder ausgewählt",
         "upload_ready": "Bereit zum Hochladen",
-        "upload_submit": "Foto hochladen",
+        "upload_submit": "Bilder hochladen",
+        "upload_progress": "{uploaded} von {total} Bildern hochgeladen",
+        "upload_in_progress": "Upload läuft – bitte diese Seite geöffnet lassen.",
+        "upload_retry": "Upload fortsetzen",
+        "upload_batch_failed": "Der Upload wurde unterbrochen. Bereits hochgeladene Bilder bleiben gespeichert.",
         "schedule": "Ablauf",
         "hotels": "Hotels",
         "taxi": "Genuss",
@@ -476,6 +489,9 @@ TEXTS = {
         "gallery_uploader_selected": "{count} ausgewählt",
         "gallery_image_alt": "Upload von {name}",
         "gallery_save_hint": "Tipp: Halte das Bild länger gedrückt, um es in deiner Mediathek zu speichern.",
+        "gallery_delete_title": "Bild löschen",
+        "gallery_delete_confirm": "Möchtest du dieses Bild wirklich löschen?",
+        "gallery_delete_cancel": "Abbrechen",
         "flash_enter_group_name": "Bitte Gruppenname eingeben.",
         "flash_invalid_group_login": "Ungültiger Gruppenname oder Passwort.",
         "flash_rsvp_select": "Bitte für alle Mitglieder eine RSVP-Auswahl treffen.",
@@ -483,7 +499,7 @@ TEXTS = {
         "flash_rsvp_age_invalid": "Bitte ein gültiges Alter (0-17) für {name} angeben.",
         "flash_rsvp_saved": "Antwort gespeichert.",
         "flash_select_image": "Bitte eine Bilddatei auswählen.",
-        "flash_allowed_types": "Nur JPG/JPEG/PNG/HEIC/HEIF sind erlaubt.",
+        "flash_allowed_types": "Nur JPG/JPEG/PNG/GIF/HEIC/HEIF sind erlaubt.",
         "flash_upload_success_count": "{count} Bilder erfolgreich hochgeladen.",
         "flash_upload_too_large": "Upload zu groß. Bitte in kleineren Paketen hochladen (max. {max_mb} MB pro Anfrage).",
         "flash_upload_failed": "Upload fehlgeschlagen. Bitte erneut versuchen.",
@@ -604,7 +620,11 @@ TEXTS = {
         "upload_multi_hint": "You can select multiple images at once or add more file fields.",
         "upload_selected_count": "{count} images selected",
         "upload_ready": "Ready to upload",
-        "upload_submit": "Upload photo",
+        "upload_submit": "Upload photos",
+        "upload_progress": "{uploaded} of {total} images uploaded",
+        "upload_in_progress": "Upload in progress – please keep this page open.",
+        "upload_retry": "Continue upload",
+        "upload_batch_failed": "The upload was interrupted. Images already uploaded remain saved.",
         "schedule": "Schedule",
         "hotels": "Hotels",
         "taxi": "Culinary Delights",
@@ -758,6 +778,9 @@ TEXTS = {
         "gallery_uploader_selected": "{count} selected",
         "gallery_image_alt": "Uploaded by {name}",
         "gallery_save_hint": "Tip: Touch and hold the photo to save it to your photo library.",
+        "gallery_delete_title": "Delete photo",
+        "gallery_delete_confirm": "Are you sure you want to delete this photo?",
+        "gallery_delete_cancel": "Cancel",
         "flash_enter_group_name": "Please enter group name.",
         "flash_invalid_group_login": "Invalid group name or password.",
         "flash_rsvp_select": "Please choose RSVP values for all members.",
@@ -765,7 +788,7 @@ TEXTS = {
         "flash_rsvp_age_invalid": "Please enter a valid age (0-17) for {name}.",
         "flash_rsvp_saved": "RSVP saved.",
         "flash_select_image": "Please select an image file.",
-        "flash_allowed_types": "Only JPG/JPEG/PNG/HEIC/HEIF are allowed.",
+        "flash_allowed_types": "Only JPG/JPEG/PNG/GIF/HEIC/HEIF are allowed.",
         "flash_upload_success_count": "{count} images uploaded successfully.",
         "flash_upload_too_large": "Upload too large. Please upload smaller batches (max {max_mb} MB per request).",
         "flash_upload_failed": "Upload failed. Please try again.",
@@ -1171,7 +1194,10 @@ def admin_required(view):
 @app.errorhandler(RequestEntityTooLarge)
 def handle_request_too_large(_error):
     max_mb = max(1, int(app.config.get("MAX_CONTENT_LENGTH", 0)) // (1024 * 1024))
-    flash(t("flash_upload_too_large").format(max_mb=max_mb))
+    message = t("flash_upload_too_large").format(max_mb=max_mb)
+    if request.headers.get("X-Upload-Batch") == "1":
+        return jsonify(ok=False, error=message), 413
+    flash(message)
     if request.method == "POST":
         return redirect(url_for("upload"))
     return redirect(url_for("landing"))
@@ -1181,6 +1207,56 @@ def is_allowed_file(filename: str) -> bool:
     return "." in filename and filename.rsplit(".", 1)[1].lower() in ALLOWED_EXTENSIONS
 
 
+def upload_error_response(message: str, status: int = 400):
+    if request.headers.get("X-Upload-Batch") == "1":
+        return jsonify(ok=False, error=message), status
+    flash(message)
+    return redirect(url_for("upload"))
+
+
+def thumbnail_filename(filename: str) -> str | None:
+    if Path(filename).name != filename or "." not in filename:
+        return None
+    extension = filename.rsplit(".", 1)[1].lower()
+    if extension not in THUMBNAIL_EXTENSIONS:
+        return None
+    return f"{filename.rsplit('.', 1)[0]}.webp"
+
+
+def ensure_thumbnail(filename: str) -> str | None:
+    thumbnail_name = thumbnail_filename(filename)
+    if thumbnail_name is None:
+        return None
+
+    source_path = Path(app.config["UPLOAD_FOLDER"]) / filename
+    thumbnail_dir = Path(app.config["THUMBNAIL_FOLDER"])
+    thumbnail_path = thumbnail_dir / thumbnail_name
+    if thumbnail_path.is_file():
+        return thumbnail_name
+    if not source_path.is_file():
+        return None
+
+    thumbnail_dir.mkdir(parents=True, exist_ok=True)
+    temporary_path = thumbnail_dir / f".{thumbnail_name}.{uuid.uuid4().hex}.tmp"
+    try:
+        with Image.open(source_path) as source_image:
+            preview = ImageOps.exif_transpose(source_image)
+            if preview.mode not in {"RGB", "RGBA"}:
+                preview = preview.convert("RGBA" if "transparency" in preview.info else "RGB")
+            preview.thumbnail(THUMBNAIL_MAX_SIZE, Image.Resampling.LANCZOS)
+            preview.save(temporary_path, format="WEBP", quality=84, method=4)
+        os.replace(temporary_path, thumbnail_path)
+        return thumbnail_name
+    except (OSError, UnidentifiedImageError, ValueError):
+        app.logger.warning("Could not create thumbnail for %s", filename, exc_info=True)
+        return None
+    finally:
+        try:
+            temporary_path.unlink()
+        except FileNotFoundError:
+            pass
+
+
 @app.get("/health")
 def health():
     return {"status": "ok"}
@@ -1409,34 +1485,35 @@ def rsvp():
 @login_required
 def upload():
     if request.method == "POST":
+        saved_paths = []
         try:
             files = [f for f in request.files.getlist("photo") if f and f.filename]
             if not files:
-                flash(t("flash_select_image"))
-                return redirect(url_for("upload"))
+                return upload_error_response(t("flash_select_image"))
 
+            validated_files = []
             for file in files:
                 if not is_allowed_file(file.filename):
-                    flash(t("flash_allowed_types"))
-                    return redirect(url_for("upload"))
+                    return upload_error_response(t("flash_allowed_types"))
                 mime_type = (file.mimetype or "").lower()
                 if mime_type and mime_type not in ALLOWED_MIME_TYPES:
-                    flash(t("flash_allowed_types"))
-                    return redirect(url_for("upload"))
+                    return upload_error_response(t("flash_allowed_types"))
+                safe_name = secure_filename(file.filename)
+                if "." not in safe_name:
+                    return upload_error_response(t("flash_allowed_types"))
+                validated_files.append((file, safe_name.rsplit(".", 1)[1].lower()))
 
             upload_dir = app.config["UPLOAD_FOLDER"]
             os.makedirs(upload_dir, exist_ok=True)
             db = get_db()
             now = datetime.utcnow().isoformat()
             upload_rows = []
-            for file in files:
-                safe_name = secure_filename(file.filename)
-                if "." not in safe_name:
-                    flash(t("flash_allowed_types"))
-                    return redirect(url_for("upload"))
-                ext = safe_name.rsplit(".", 1)[1].lower()
+            for file, ext in validated_files:
                 stored_name = f"{uuid.uuid4().hex}.{ext}"
-                file.save(os.path.join(upload_dir, stored_name))
+                stored_path = os.path.join(upload_dir, stored_name)
+                file.save(stored_path)
+                saved_paths.append(stored_path)
+                ensure_thumbnail(stored_name)
                 upload_rows.append((stored_name, int(session["group_id"]), now))
 
             db.executemany(
@@ -1445,14 +1522,20 @@ def upload():
             )
             db.commit()
 
+            if request.headers.get("X-Upload-Batch") == "1":
+                return jsonify(ok=True, count=len(upload_rows))
             flash(t("flash_upload_success_count").format(count=len(upload_rows)))
             return redirect(url_for("gallery"))
         except RequestEntityTooLarge:
             raise
         except Exception:
             app.logger.exception("Upload failed")
-            flash(t("flash_upload_failed"))
-            return redirect(url_for("upload"))
+            for saved_path in saved_paths:
+                try:
+                    os.remove(saved_path)
+                except FileNotFoundError:
+                    pass
+            return upload_error_response(t("flash_upload_failed"), 500)
 
     return render_template("upload.html")
 
@@ -1500,6 +1583,11 @@ def delete_image(image_id: int):
     file_path = os.path.join(app.config["UPLOAD_FOLDER"], image["filename"])
     if os.path.isfile(file_path):
         os.remove(file_path)
+    thumbnail_name = thumbnail_filename(str(image["filename"]))
+    if thumbnail_name:
+        thumbnail_path = os.path.join(app.config["THUMBNAIL_FOLDER"], thumbnail_name)
+        if os.path.isfile(thumbnail_path):
+            os.remove(thumbnail_path)
 
     flash(t("flash_image_deleted"))
     return redirect(url_for("gallery"))
@@ -1517,6 +1605,19 @@ def serve_upload(filename: str):
     )
 
 
+@app.get("/uploads/thumbnails/<path:filename>")
+@login_required
+def serve_thumbnail(filename: str):
+    generated_name = ensure_thumbnail(filename)
+    if generated_name:
+        return send_from_directory(
+            app.config["THUMBNAIL_FOLDER"],
+            generated_name,
+            max_age=31536000,
+        )
+    return send_from_directory(app.config["UPLOAD_FOLDER"], filename)
+
+
 @app.get("/info/<page>")
 @login_required
 def info(page: str):
diff --git a/backend/static/styles.css b/backend/static/styles.css
index ffde7fb..3344695 100644
--- a/backend/static/styles.css
+++ b/backend/static/styles.css
@@ -634,6 +634,64 @@ input[type="file"]:focus {
   padding: 0;
 }
 
+.upload-progress {
+  padding: 0.85rem 1rem;
+  border: 1px solid rgba(31, 58, 47, 0.14);
+  border-radius: 14px;
+  background: rgba(255, 253, 248, 0.9);
+}
+
+.upload-progress[hidden] {
+  display: none;
+}
+
+.upload-progress-track {
+  height: 0.65rem;
+  overflow: hidden;
+  border-radius: 999px;
+  background: rgba(31, 58, 47, 0.12);
+}
+
+.upload-progress-track span {
+  display: block;
+  width: 0;
+  height: 100%;
+  border-radius: inherit;
+  background: linear-gradient(90deg, var(--gold), var(--forest));
+  transition: width 0.25s ease;
+}
+
+.upload-progress-count {
+  margin: 0.65rem 0 0;
+  color: var(--forest);
+  font-weight: 700;
+  text-align: center;
+}
+
+.upload-progress-status {
+  margin: 0.2rem 0 0;
+  color: rgba(31, 31, 31, 0.7);
+  text-align: center;
+}
+
+.upload-progress-status.is-error {
+  color: var(--burgundy);
+}
+
+.upload-retry-btn[hidden] {
+  display: none;
+}
+
+.form-grid.is-uploading .upload-picker {
+  cursor: wait;
+  opacity: 0.62;
+}
+
+.upload-file-remove:disabled {
+  cursor: not-allowed;
+  opacity: 0.45;
+}
+
 .btn {
   display: inline-flex;
   align-items: center;
@@ -1466,6 +1524,43 @@ input[type="file"]:focus {
   background: #5e2733;
 }
 
+.gallery-delete-dialog {
+  width: min(24rem, calc(100% - 2rem));
+  margin: auto;
+  padding: 1.5rem;
+  border: 1px solid rgba(109, 47, 61, 0.2);
+  border-radius: 18px;
+  background: #fffdf8;
+  color: var(--forest);
+  text-align: center;
+  box-shadow: 0 22px 60px rgba(18, 31, 24, 0.3);
+}
+
+.gallery-delete-dialog::backdrop {
+  background: rgba(18, 31, 24, 0.62);
+  backdrop-filter: blur(2px);
+}
+
+.gallery-delete-dialog h2 {
+  margin: 0 0 0.65rem;
+}
+
+.gallery-delete-dialog p {
+  margin: 0;
+}
+
+.gallery-delete-dialog-actions {
+  display: flex;
+  flex-wrap: wrap;
+  justify-content: center;
+  gap: 0.75rem;
+  margin-top: 1.35rem;
+}
+
+.gallery-delete-dialog-actions .btn {
+  min-width: 7.5rem;
+}
+
 .lightbox {
   position: fixed;
   inset: 0;
diff --git a/backend/templates/gallery.html b/backend/templates/gallery.html
index 3f12cb3..845fbcd 100644
--- a/backend/templates/gallery.html
+++ b/backend/templates/gallery.html
@@ -47,10 +47,14 @@
           class="gallery-open"
           data-image-index="{{ loop.index0 }}"
         >
-          <img src="{{ url_for('serve_upload', filename=image['filename']) }}" alt="{{ t('gallery_image_alt').format(name=image['uploaded_by_name']) }}" loading="lazy" />
+          <img src="{{ url_for('serve_thumbnail', filename=image['filename']) }}" alt="{{ t('gallery_image_alt').format(name=image['uploaded_by_name']) }}" loading="lazy" />
         </a>
         {% if is_host or guest_id == image['uploaded_by'] %}
-        <form class="gallery-delete-form" method="post" action="{{ url_for('delete_image', image_id=image['id']) }}">
+        <form
+          class="gallery-delete-form"
+          method="post"
+          action="{{ url_for('delete_image', image_id=image['id']) }}"
+        >
           <button class="gallery-delete-btn" type="submit" aria-label="{{ t('delete') }}" title="{{ t('delete') }}">
             <svg viewBox="0 0 24 24" aria-hidden="true" focusable="false">
               <path d="M9 3h6l1 2h4v2H4V5h4l1-2zm1 6h2v8h-2V9zm4 0h2v8h-2V9zM7 9h2v8H7V9z" />
@@ -82,8 +86,45 @@
     <div class="lightbox-save-hint" id="lightbox-save-hint" role="status">{{ t('gallery_save_hint') }}</div>
   </div>
 
+  <dialog class="gallery-delete-dialog" id="gallery-delete-dialog" aria-labelledby="gallery-delete-title" aria-describedby="gallery-delete-message">
+    <h2 id="gallery-delete-title">{{ t('gallery_delete_title') }}</h2>
+    <p id="gallery-delete-message">{{ t('gallery_delete_confirm') }}</p>
+    <div class="gallery-delete-dialog-actions">
+      <button class="btn btn-ghost" id="gallery-delete-cancel" type="button">{{ t('gallery_delete_cancel') }}</button>
+      <button class="btn btn-danger" id="gallery-delete-confirm" type="button">{{ t('delete') }}</button>
+    </div>
+  </dialog>
+
   <script>
     (() => {
+      const deleteDialog = document.getElementById("gallery-delete-dialog");
+      const deleteCancel = document.getElementById("gallery-delete-cancel");
+      const deleteConfirm = document.getElementById("gallery-delete-confirm");
+      let pendingDeleteForm = null;
+
+      document.querySelectorAll(".gallery-delete-form").forEach((form) => {
+        form.addEventListener("submit", (event) => {
+          event.preventDefault();
+          pendingDeleteForm = form;
+          deleteDialog.showModal();
+        });
+      });
+
+      deleteCancel.addEventListener("click", () => deleteDialog.close());
+      deleteConfirm.addEventListener("click", () => {
+        if (pendingDeleteForm) {
+          HTMLFormElement.prototype.submit.call(pendingDeleteForm);
+        }
+      });
+      deleteDialog.addEventListener("close", () => {
+        pendingDeleteForm = null;
+      });
+      deleteDialog.addEventListener("click", (event) => {
+        if (event.target === deleteDialog) {
+          deleteDialog.close();
+        }
+      });
+
       const lightbox = document.getElementById("gallery-lightbox");
       const lightboxImage = document.getElementById("lightbox-image");
       const lightboxDownload = document.getElementById("lightbox-download");
diff --git a/backend/templates/upload.html b/backend/templates/upload.html
index d0c3684..d045951 100644
--- a/backend/templates/upload.html
+++ b/backend/templates/upload.html
@@ -7,12 +7,27 @@
     <label class="upload-picker" for="photo-input">
       <span class="upload-picker-title">{{ t('file') }}</span>
       <span class="upload-picker-subtitle">{{ t('upload_picker_hint') }}</span>
-      <input id="photo-input" class="sr-only" type="file" name="photo" accept="image/jpeg,image/png,image/jpg,image/heic,image/heif,.heic,.heif" multiple />
+      <input id="photo-input" class="sr-only" type="file" name="photo" accept="image/jpeg,image/png,image/jpg,image/gif,image/heic,image/heif,.gif,.heic,.heif" multiple />
     </label>
     <p id="upload-selected-count" class="upload-count"></p>
     <p id="upload-ready-hint" class="upload-ready">{{ t('upload_ready') }}</p>
     <ul id="upload-file-list" class="upload-file-list"></ul>
+    <div id="upload-progress" class="upload-progress" hidden>
+      <div
+        id="upload-progress-track"
+        class="upload-progress-track"
+        role="progressbar"
+        aria-valuemin="0"
+        aria-valuemax="100"
+        aria-valuenow="0"
+      >
+        <span id="upload-progress-bar"></span>
+      </div>
+      <p id="upload-progress-count" class="upload-progress-count" aria-live="polite"></p>
+      <p id="upload-progress-status" class="upload-progress-status">{{ t('upload_in_progress') }}</p>
+    </div>
     <button id="upload-submit-btn" class="btn" type="submit" disabled>{{ t('upload_submit') }}</button>
+    <button id="upload-retry-btn" class="btn upload-retry-btn" type="button" hidden>{{ t('upload_retry') }}</button>
   </form>
 </section>
 
@@ -24,17 +39,27 @@
     const readyEl = document.getElementById("upload-ready-hint");
     const listEl = document.getElementById("upload-file-list");
     const submitBtn = document.getElementById("upload-submit-btn");
+    const retryBtn = document.getElementById("upload-retry-btn");
+    const progressEl = document.getElementById("upload-progress");
+    const progressTrack = document.getElementById("upload-progress-track");
+    const progressBar = document.getElementById("upload-progress-bar");
+    const progressCount = document.getElementById("upload-progress-count");
+    const progressStatus = document.getElementById("upload-progress-status");
     const countTpl = {{ t('upload_selected_count')|tojson }};
+    const progressTpl = {{ t('upload_progress')|tojson }};
+    const inProgressText = {{ t('upload_in_progress')|tojson }};
+    const batchFailedText = {{ t('upload_batch_failed')|tojson }};
+    const galleryUrl = {{ url_for('gallery')|tojson }};
+    const maxBatchFiles = 10;
+    const maxBatchBytes = 40 * 1024 * 1024;
     const selectedFiles = [];
+    let remainingFiles = [];
+    let totalFiles = 0;
+    let uploadedFiles = 0;
+    let isUploading = false;
 
     const fileKey = (file) => `${file.name}__${file.size}__${file.lastModified}`;
 
-    const syncInputFiles = () => {
-      const transfer = new DataTransfer();
-      selectedFiles.forEach((file) => transfer.items.add(file));
-      fileInput.files = transfer.files;
-    };
-
     const renderSelection = () => {
       if (!selectedFiles.length) {
         countEl.textContent = "";
@@ -54,7 +79,7 @@
         readyEl.classList.add("is-visible");
       }
       if (submitBtn) {
-        submitBtn.disabled = false;
+        submitBtn.disabled = isUploading;
       }
 
       selectedFiles.slice(0, 20).forEach((file, index) => {
@@ -69,7 +94,6 @@
         removeBtn.textContent = "×";
         removeBtn.addEventListener("click", () => {
           selectedFiles.splice(index, 1);
-          syncInputFiles();
           renderSelection();
         });
 
@@ -93,18 +117,105 @@
           existingKeys.add(key);
         }
       });
-      syncInputFiles();
       fileInput.value = "";
       renderSelection();
     });
 
+    const updateProgress = () => {
+      const percent = totalFiles ? Math.round((uploadedFiles / totalFiles) * 100) : 0;
+      progressBar.style.width = `${percent}%`;
+      progressTrack.setAttribute("aria-valuenow", String(percent));
+      progressCount.textContent = progressTpl
+        .replace("{uploaded}", String(uploadedFiles))
+        .replace("{total}", String(totalFiles));
+    };
+
+    const nextBatch = () => {
+      let batchSize = 0;
+      let batchLength = 0;
+      while (batchLength < remainingFiles.length && batchLength < maxBatchFiles) {
+        const nextSize = remainingFiles[batchLength].size;
+        if (batchLength > 0 && batchSize + nextSize > maxBatchBytes) {
+          break;
+        }
+        batchSize += nextSize;
+        batchLength += 1;
+      }
+      return remainingFiles.slice(0, batchLength);
+    };
+
+    const setUploadLocked = (locked) => {
+      fileInput.disabled = locked;
+      submitBtn.disabled = locked;
+      document.querySelectorAll(".upload-file-remove").forEach((button) => {
+        button.disabled = locked;
+      });
+      form.classList.toggle("is-uploading", locked);
+    };
+
+    const uploadRemainingFiles = async () => {
+      if (isUploading || !remainingFiles.length) return;
+      isUploading = true;
+      setUploadLocked(true);
+      retryBtn.hidden = true;
+      progressEl.hidden = false;
+      progressStatus.textContent = inProgressText;
+      progressStatus.classList.remove("is-error");
+      updateProgress();
+
+      try {
+        while (remainingFiles.length) {
+          const batch = nextBatch();
+          const body = new FormData();
+          batch.forEach((file) => body.append("photo", file, file.name));
+          const response = await fetch(form.action || window.location.href, {
+            method: "POST",
+            body,
+            credentials: "same-origin",
+            headers: { "X-Upload-Batch": "1" }
+          });
+          const contentType = response.headers.get("content-type") || "";
+          const payload = contentType.includes("application/json") ? await response.json() : null;
+          if (!response.ok || !payload || !payload.ok) {
+            throw new Error(payload?.error || batchFailedText);
+          }
+          remainingFiles.splice(0, batch.length);
+          uploadedFiles += batch.length;
+          updateProgress();
+        }
+        window.location.assign(galleryUrl);
+      } catch (error) {
+        progressStatus.textContent = `${batchFailedText} ${error.message || ""}`.trim();
+        progressStatus.classList.add("is-error");
+        retryBtn.hidden = false;
+      } finally {
+        isUploading = false;
+        form.classList.remove("is-uploading");
+        if (remainingFiles.length) {
+          fileInput.disabled = true;
+          submitBtn.disabled = true;
+        }
+      }
+    };
+
     form.addEventListener("submit", (event) => {
-      if (!selectedFiles.length) {
-        event.preventDefault();
+      event.preventDefault();
+      if (!selectedFiles.length || isUploading) {
         renderSelection();
         return;
       }
-      syncInputFiles();
+      totalFiles = selectedFiles.length;
+      uploadedFiles = 0;
+      remainingFiles = [...selectedFiles];
+      uploadRemainingFiles();
+    });
+
+    retryBtn.addEventListener("click", uploadRemainingFiles);
+
+    window.addEventListener("beforeunload", (event) => {
+      if (!isUploading) return;
+      event.preventDefault();
+      event.returnValue = "";
     });
 
     renderSelection();
diff --git a/data/db/app.sqlite3 b/data/db/app.sqlite3
index 47715bd..21fac1e 100644
Binary files a/data/db/app.sqlite3 and b/data/db/app.sqlite3 differ
diff --git a/docker-compose.yml b/docker-compose.yml
index 52e78e5..6008ed1 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -23,6 +23,7 @@ services:
     environment:
       - DB_PATH=/app/db/app.sqlite3
       - UPLOAD_FOLDER=/app/uploads
+      - THUMBNAIL_FOLDER=/app/uploads/thumbnails
       - EVENT_PASSWORD=${EVENT_PASSWORD:-wedding2026}
       - HOST_PASSWORD=${HOST_PASSWORD:-gastgeber2026}
       - PHOTOGRAPHER_PASSWORD=${PHOTOGRAPHER_PASSWORD:-Foto!Graf26#}