diff --git a/backend/app/admin_ui.py b/backend/app/admin_ui.py
index 04c6db4..e108d3d 100644
--- a/backend/app/admin_ui.py
+++ b/backend/app/admin_ui.py
@@ -3,6 +3,7 @@ from __future__ import annotations
 import json
 from pathlib import Path
 import re
+from urllib.parse import urlparse
 from urllib.parse import urlencode
 from urllib.request import Request as UrlRequest, urlopen
 
@@ -124,6 +125,14 @@ def _is_probably_irrelevant_image(url: str) -> bool:
     return any(re.search(pattern, lowered) for pattern in patterns)
 
 
+def _is_http_image_url(url: str) -> bool:
+    try:
+        parsed = urlparse(url)
+    except Exception:
+        return False
+    return parsed.scheme in {"http", "https"} and bool(parsed.netloc)
+
+
 def _build_image_entries(article: dict, extraction: dict, meta: dict) -> list[dict[str, object]]:
     all_images = _read_article_images(article, extraction)
     image_review = meta.get("image_review") if isinstance(meta.get("image_review"), dict) else {}
@@ -371,15 +380,19 @@ def admin_article_image_decision(
 
 @router.get("/admin/images/proxy")
 def admin_image_proxy(request: Request, url: str):
-    user = _admin_user(request)
-    if not user:
-        return Response(status_code=401)
-
-    if not (url.startswith("http://") or url.startswith("https://")):
+    if not _is_http_image_url(url):
         return Response(status_code=400)
 
     try:
-        req = UrlRequest(url=url, headers={"User-Agent": IMAGE_PROXY_USER_AGENT, "Referer": url})
+        referer = request.headers.get("referer", "")
+        req = UrlRequest(
+            url=url,
+            headers={
+                "User-Agent": IMAGE_PROXY_USER_AGENT,
+                "Accept": "image/avif,image/webp,image/apng,image/*,*/*;q=0.8",
+                "Referer": referer or url,
+            },
+        )
         with urlopen(req, timeout=10) as resp:
             body = resp.read()
             content_type = resp.headers.get("Content-Type", "application/octet-stream")
diff --git a/backend/static/admin.css b/backend/static/admin.css
index 402c067..705aeda 100644
--- a/backend/static/admin.css
+++ b/backend/static/admin.css
@@ -210,6 +210,11 @@ button.secondary {
   background: #f8fafc;
 }
 
+.img-failed {
+  opacity: 0.3;
+  filter: grayscale(1);
+}
+
 .image-meta {
   margin-top: 6px;
   display: flex;
diff --git a/backend/templates/admin_article_detail.html b/backend/templates/admin_article_detail.html
index bdfc0af..a38937b 100644
--- a/backend/templates/admin_article_detail.html
+++ b/backend/templates/admin_article_detail.html
@@ -79,7 +79,7 @@
         {% for image in article.image_entries %}
         <article class="image-card {{ 'image-selected' if image.is_selected else '' }} {{ 'image-excluded' if image.is_excluded else '' }}">
           <a href="{{ image.url }}" target="_blank" rel="noopener">
-            <img src="{{ image.proxy_url }}" alt="Artikelbild" loading="lazy" />
+            <img src="{{ image.proxy_url }}" data-fallback-src="{{ image.url }}" alt="Artikelbild" loading="lazy" onerror="if(!this.dataset.fallbackUsed){this.dataset.fallbackUsed='1';this.src=this.dataset.fallbackSrc;}else{this.classList.add('img-failed');}" />
           </a>
           <div class="image-meta">
             {% if image.is_selected %}<span class="badge ok">Ausgewählt</span>{% endif %}
diff --git a/backend/templates/admin_dashboard.html b/backend/templates/admin_dashboard.html
index 6709f65..5dad3f5 100644
--- a/backend/templates/admin_dashboard.html
+++ b/backend/templates/admin_dashboard.html
@@ -157,7 +157,7 @@
               <div class="subtle">Legal: {{ "OK" if a.legal_checked else "offen" }}</div>
               {% if a.selected_image_url %}
               <div class="subtle">Hauptbild gesetzt</div>
-              <a href="{{ a.selected_image_url }}" target="_blank" rel="noopener"><img src="{{ a.selected_image_proxy_url }}" alt="Hauptbild" class="thumb" loading="lazy" /></a>
+              <a href="{{ a.selected_image_url }}" target="_blank" rel="noopener"><img src="{{ a.selected_image_proxy_url }}" data-fallback-src="{{ a.selected_image_url }}" alt="Hauptbild" class="thumb" loading="lazy" onerror="if(!this.dataset.fallbackUsed){this.dataset.fallbackUsed='1';this.src=this.dataset.fallbackSrc;}else{this.classList.add('img-failed');}" /></a>
               {% endif %}
               {% if a.summary %}
               <div><strong>Summary:</strong> {{ a.summary }}</div>