diff --git a/README.md b/README.md
index 1796d73..6e5709b 100644
--- a/README.md
+++ b/README.md
@@ -499,6 +499,28 @@ server {
 }
 ```
 
+#### Don't add security headers at the proxy
+
+The app already sets `X-Frame-Options`, `Strict-Transport-Security`, `Content-Security-Policy`,
+`X-Content-Type-Options`, etc. via [helmet](https://helmetjs.github.io/), and manages them
+**per route**: widget/kiosk renders and the device preview deliberately remove or relax
+`X-Frame-Options` so they can be framed, while the dashboard keeps the strict policy.
+
+A proxy-level header block (nginx `add_header X-Frame-Options DENY;`, a Caddy
+`header { ... }` snippet, or a "security headers" preset) *adds a second copy* of these
+headers on top of the app's. Browsers treat conflicting duplicate `X-Frame-Options`
+values as `deny`, which breaks the dashboard's device Preview (a same-origin iframe of
+`/player`) and widget previews with console errors like:
+
+```
+Refused to display 'https://…' in a frame because it set multiple
+'X-Frame-Options' headers with conflicting values ('DENY, SAMEORIGIN').
+Falling back to 'deny'.
+```
+
+Let the proxy handle TLS, compression, and body-size limits only, and leave security
+headers to the app.
+
 ### Updating
 
 To update a running instance to the latest version:
diff --git a/frontend/js/i18n/de.js b/frontend/js/i18n/de.js
index 8429af2..2fe1010 100644
--- a/frontend/js/i18n/de.js
+++ b/frontend/js/i18n/de.js
@@ -347,6 +347,9 @@ export default {
   'device.assign.select_first': 'Erst etwas auswählen',
   'device.assign.kiosk_widget_name': 'Kiosk: {name}',
   'device.toast.screenshot_requested': 'Screenshot angefordert',
+  'device.toast.screenshot_unsupported': 'Der Player dieses Displays unterstützt keine Screenshots',
+  'device.toast.screenshot_offline': 'Display ist offline — Screenshot nicht angefordert',
+  'device.toast.screenshot_failed': 'Screenshot-Anfrage fehlgeschlagen — keine Antwort vom Server',
   'device.toast.renamed': 'Bildschirm umbenannt',
   'device.toast.removing': 'Wird entfernt...',
   'device.toast.removed': 'Bildschirm entfernt',
diff --git a/frontend/js/i18n/en.js b/frontend/js/i18n/en.js
index 821c15d..adcdaef 100644
--- a/frontend/js/i18n/en.js
+++ b/frontend/js/i18n/en.js
@@ -648,6 +648,9 @@ export default {
   'device.assign.kiosk_widget_name': 'Kiosk: {name}',
   // Toasts
   'device.toast.screenshot_requested': 'Screenshot requested',
+  'device.toast.screenshot_unsupported': 'This display\'s player can\'t take screenshots',
+  'device.toast.screenshot_offline': 'Display is offline — screenshot not requested',
+  'device.toast.screenshot_failed': 'Screenshot request failed — no response from server',
   'device.toast.renamed': 'Display renamed',
   'device.toast.removing': 'Removing...',
   'device.toast.removed': 'Display removed',
diff --git a/frontend/js/i18n/es.js b/frontend/js/i18n/es.js
index 9a6da03..ca1c47d 100644
--- a/frontend/js/i18n/es.js
+++ b/frontend/js/i18n/es.js
@@ -377,6 +377,9 @@ export default {
   'device.assign.select_first': 'Primero selecciona algo',
   'device.assign.kiosk_widget_name': 'Kiosco: {name}',
   'device.toast.screenshot_requested': 'Captura solicitada',
+  'device.toast.screenshot_unsupported': 'El reproductor de esta pantalla no admite capturas de pantalla',
+  'device.toast.screenshot_offline': 'La pantalla está desconectada — captura no solicitada',
+  'device.toast.screenshot_failed': 'La solicitud de captura falló — sin respuesta del servidor',
   'device.toast.renamed': 'Pantalla renombrada',
   'device.toast.removing': 'Eliminando...',
   'device.toast.removed': 'Pantalla eliminada',
diff --git a/frontend/js/i18n/fr.js b/frontend/js/i18n/fr.js
index 438f36c..8acb3ec 100644
--- a/frontend/js/i18n/fr.js
+++ b/frontend/js/i18n/fr.js
@@ -347,6 +347,9 @@ export default {
   'device.assign.select_first': 'Sélectionnez d\'abord un élément',
   'device.assign.kiosk_widget_name': 'Kiosque : {name}',
   'device.toast.screenshot_requested': 'Capture demandée',
+  'device.toast.screenshot_unsupported': 'Le lecteur de cet écran ne prend pas en charge les captures d\'écran',
+  'device.toast.screenshot_offline': 'Écran hors ligne — capture non demandée',
+  'device.toast.screenshot_failed': 'Échec de la demande de capture — pas de réponse du serveur',
   'device.toast.renamed': 'Écran renommé',
   'device.toast.removing': 'Suppression...',
   'device.toast.removed': 'Écran retiré',
diff --git a/frontend/js/i18n/it.js b/frontend/js/i18n/it.js
index 091c2d9..c5ad537 100644
--- a/frontend/js/i18n/it.js
+++ b/frontend/js/i18n/it.js
@@ -371,6 +371,9 @@ export default {
   'device.assign.kiosk_widget_name': 'Chiosco: {name}',
   // Toasts
   'device.toast.screenshot_requested': 'Richiesta screenshot inviata',
+  'device.toast.screenshot_unsupported': 'Il player di questo schermo non supporta gli screenshot',
+  'device.toast.screenshot_offline': 'Lo schermo è offline — screenshot non richiesto',
+  'device.toast.screenshot_failed': 'Richiesta screenshot non riuscita — nessuna risposta dal server',
   'device.toast.renamed': 'Schermo rinominato',
   'device.toast.removing': 'Rimozione in corso...',
   'device.toast.removed': 'Schermo rimosso',
diff --git a/frontend/js/i18n/pt.js b/frontend/js/i18n/pt.js
index e7a90d5..3dcd64a 100644
--- a/frontend/js/i18n/pt.js
+++ b/frontend/js/i18n/pt.js
@@ -347,6 +347,9 @@ export default {
   'device.assign.select_first': 'Selecione algo primeiro',
   'device.assign.kiosk_widget_name': 'Quiosque: {name}',
   'device.toast.screenshot_requested': 'Captura solicitada',
+  'device.toast.screenshot_unsupported': 'O player desta tela não suporta capturas de tela',
+  'device.toast.screenshot_offline': 'A tela está offline — captura não solicitada',
+  'device.toast.screenshot_failed': 'Falha na solicitação de captura — sem resposta do servidor',
   'device.toast.renamed': 'Tela renomeada',
   'device.toast.removing': 'Removendo...',
   'device.toast.removed': 'Tela removida',
diff --git a/frontend/js/socket.js b/frontend/js/socket.js
index a1e5840..e5e2d20 100644
--- a/frontend/js/socket.js
+++ b/frontend/js/socket.js
@@ -112,9 +112,22 @@ function emit(event, data) {
   if (cbs) cbs.forEach(cb => cb(data));
 }
 
-export function requestScreenshot(deviceId) {
+// Optional callback receives the server-side ack: { delivered, reason, capability }.
+// reason is 'offline' (no live connection) or 'unsupported' (this player type can't
+// take screenshots). Callers without a callback keep firing-and-forgetting — the
+// dashboard grid and the device-detail 5s poll stay silent; only the explicit
+// Screenshot button asks for the verdict.
+export function requestScreenshot(deviceId, callback) {
   console.log('requestScreenshot:', deviceId, 'socket connected:', dashboardSocket?.connected);
-  if (dashboardSocket) dashboardSocket.emit('dashboard:request-screenshot', { device_id: deviceId });
+  if (!dashboardSocket) return;
+  if (typeof callback === 'function') {
+    dashboardSocket.timeout(5000).emit('dashboard:request-screenshot', { device_id: deviceId }, (err, ack) => {
+      if (err) callback({ delivered: false, reason: 'no_ack' });
+      else callback(ack || { delivered: false, reason: 'no_ack' });
+    });
+  } else {
+    dashboardSocket.emit('dashboard:request-screenshot', { device_id: deviceId });
+  }
 }
 
 export function startRemote(deviceId) {
diff --git a/frontend/js/views/device-detail.js b/frontend/js/views/device-detail.js
index 32e6fba..7a26256 100644
--- a/frontend/js/views/device-detail.js
+++ b/frontend/js/views/device-detail.js
@@ -1084,10 +1084,16 @@ function setupActions(device) {
 
   document.getElementById('devicePreviewBtn')?.addEventListener('click', () => showDevicePreview(device));
 
-  // Screenshot button
+  // Screenshot button — pass a callback so the server's verdict surfaces as a toast
+  // instead of the request silently going nowhere (offline device, or a player type
+  // that can't capture at all, e.g. BrightSign).
   document.getElementById('screenshotBtn')?.addEventListener('click', () => {
-    requestScreenshot(device.id);
-    showToast(t('device.toast.screenshot_requested'), 'info');
+    requestScreenshot(device.id, (ack) => {
+      if (ack?.delivered) showToast(t('device.toast.screenshot_requested'), 'info');
+      else if (ack?.reason === 'unsupported') showToast(t('device.toast.screenshot_unsupported'), 'warning');
+      else if (ack?.reason === 'offline') showToast(t('device.toast.screenshot_offline'), 'warning');
+      else showToast(t('device.toast.screenshot_failed'), 'error');
+    });
   });
 
   // Rename