diff --git a/backend/src/routes/gallery.js b/backend/src/routes/gallery.js
index 1464fca3..2b5a6db6 100644
--- a/backend/src/routes/gallery.js
+++ b/backend/src/routes/gallery.js
@@ -172,7 +172,13 @@ router.get('/:slug/photos', verifyGalleryAccess, async (req, res) => {
   try {
     // Get filter parameters from query
     const { filter, guest_id } = req.query;
-    
+
+    // Get watermark settings to generate cache-busting version for URLs
+    const watermarkSettings = await watermarkService.getWatermarkSettings();
+    const wmVersion = watermarkSettings?.enabled
+      ? `wm=${watermarkSettings.opacity}${watermarkSettings.position}${watermarkSettings.size}`
+      : '';
+
     // First get all photos
     let photos = await db('photos')
       .where('photos.event_id', req.event.id)
@@ -327,15 +333,17 @@ router.get('/:slug/photos', verifyGalleryAccess, async (req, res) => {
       categories: categories,
       photos: photos.map(photo => {
         const useJwtUrl = (protectionSettings.protection_level === 'basic' || protectionSettings.protection_level === 'standard');
-        const photoUrl = useJwtUrl ? 
-          `/api/gallery/${req.params.slug}/photo/${photo.id}` : 
+        // Add watermark version to URLs for cache busting when settings change
+        const wmQuery = wmVersion ? `?${wmVersion}` : '';
+        const photoUrl = useJwtUrl ?
+          `/api/gallery/${req.params.slug}/photo/${photo.id}${wmQuery}` :
           `/api/secure-images/${req.params.slug}/secure/${photo.id}/{{token}}`;
-        
+
         return {
           id: photo.id,
           filename: photo.filename,
           url: photoUrl,
-          thumbnail_url: photo.thumbnail_path ? `/api/gallery/${req.params.slug}/thumbnail/${photo.id}` : null,
+          thumbnail_url: photo.thumbnail_path ? `/api/gallery/${req.params.slug}/thumbnail/${photo.id}${wmQuery}` : null,
           secure_url_template: `/api/secure-images/${req.params.slug}/secure/${photo.id}/{{token}}`,
           download_url_template: `/api/secure-images/${req.params.slug}/secure-download/${photo.id}/{{token}}`,
           type: photo.type,
@@ -754,6 +762,20 @@ router.get('/:slug/photo/:photoId',
       // Get watermark settings
       const watermarkSettings = await watermarkService.getWatermarkSettings();
 
+      // Generate ETag based on photo id, modification time, and watermark settings
+      // This ensures cache invalidation when watermark settings change
+      const fs = require('fs');
+      const stat = fs.statSync(filePath);
+      const watermarkHash = watermarkSettings?.enabled
+        ? `-wm${watermarkSettings.opacity}${watermarkSettings.position}${watermarkSettings.size}`
+        : '-nowm';
+      const etag = `"${photoId}-${stat.mtime.getTime()}${watermarkHash}"`;
+
+      // Check if client has valid cached version
+      if (req.headers['if-none-match'] === etag) {
+        return res.status(304).end();
+      }
+
       if (watermarkSettings && watermarkSettings.enabled) {
         // Apply watermark and send
         const watermarkedBuffer = await watermarkService.applyWatermark(filePath, watermarkSettings);
@@ -761,6 +783,7 @@ router.get('/:slug/photo/:photoId',
         res.set({
           'Content-Type': photo.mime_type || 'image/jpeg',
           'Cache-Control': 'private, max-age=1800', // Cache for 30 minutes
+          'ETag': etag,
           'X-Protection-Level': 'basic'
         });
 
@@ -769,6 +792,7 @@ router.get('/:slug/photo/:photoId',
         // Send original file with basic protection headers
         res.set({
           'Cache-Control': 'private, max-age=1800',
+          'ETag': etag,
           'X-Protection-Level': 'basic'
         });
         // Ensure absolute path for res.sendFile
@@ -820,18 +844,32 @@ router.get('/:slug/thumbnail/:photoId',
         'thumbnail'
       );
 
+      // Check if watermarks are enabled and apply to thumbnail
+      const watermarkSettings = await watermarkService.getWatermarkSettings();
+
+      // Generate ETag based on photo id, thumbnail modification time, and watermark settings
+      const fs = require('fs');
+      const stat = fs.statSync(thumbPath);
+      const watermarkHash = watermarkSettings?.enabled
+        ? `-wm${watermarkSettings.opacity}${watermarkSettings.position}${watermarkSettings.size}`
+        : '-nowm';
+      const etag = `"thumb-${photoId}-${stat.mtime.getTime()}${watermarkHash}"`;
+
+      // Check if client has valid cached version
+      if (req.headers['if-none-match'] === etag) {
+        return res.status(304).end();
+      }
+
       // Set appropriate headers with enhanced security
       res.set({
         'Content-Type': 'image/jpeg',
         'Cache-Control': 'private, max-age=1800', // Reduced cache time
         'Cross-Origin-Resource-Policy': 'cross-origin',
         'X-Content-Type-Options': 'nosniff',
-        'X-Protected-Thumbnail': 'true'
+        'X-Protected-Thumbnail': 'true',
+        'ETag': etag
       });
 
-      // Check if watermarks are enabled and apply to thumbnail
-      const watermarkSettings = await watermarkService.getWatermarkSettings();
-
       if (watermarkSettings && watermarkSettings.enabled) {
         // Apply watermark to thumbnail
         const watermarkedBuffer = await watermarkService.applyWatermark(thumbPath, watermarkSettings);
diff --git a/frontend/src/components/common/AuthenticatedImage.tsx b/frontend/src/components/common/AuthenticatedImage.tsx
index 66d52748..71ad2c2f 100644
--- a/frontend/src/components/common/AuthenticatedImage.tsx
+++ b/frontend/src/components/common/AuthenticatedImage.tsx
@@ -7,7 +7,7 @@ import {
   resolveSlugFromRequestUrl,
 } from '../../utils/galleryAuthStorage';
 
-interface AuthenticatedImageProps extends React.ImgHTMLAttributes<HTMLImageElement> {
+interface AuthenticatedImageProps extends Omit<React.ImgHTMLAttributes<HTMLImageElement>, 'onLoad'> {
   src: string;
   fallbackSrc?: string;
   useWatermark?: boolean;
@@ -29,6 +29,7 @@ interface AuthenticatedImageProps extends React.ImgHTMLAttributes<HTMLImageEleme
   detectDevTools?: boolean;
   protectionLevel?: 'basic' | 'standard' | 'enhanced' | 'maximum';
   useEnhancedProtection?: boolean;
+  onLoad?: () => void;
 }
 
 export const AuthenticatedImage: React.FC<AuthenticatedImageProps> = ({
@@ -54,6 +55,7 @@ export const AuthenticatedImage: React.FC<AuthenticatedImageProps> = ({
   detectDevTools,
   protectionLevel,
   useEnhancedProtection,
+  onLoad,
   ...props
 }) => {
   const unusedProps = {
@@ -221,6 +223,7 @@ export const AuthenticatedImage: React.FC<AuthenticatedImageProps> = ({
     img.onload = () => {
       imageRef.current = img;
       drawToCanvas();
+      onLoad?.();
     };
 
     img.onerror = (e) => {
@@ -235,7 +238,7 @@ export const AuthenticatedImage: React.FC<AuthenticatedImageProps> = ({
       img.onload = null;
       img.onerror = null;
     };
-  }, [imageSrc, useCanvasRendering, drawToCanvas]);
+  }, [imageSrc, useCanvasRendering, drawToCanvas, onLoad]);
 
   if (isLoading) {
     return (
@@ -282,5 +285,5 @@ export const AuthenticatedImage: React.FC<AuthenticatedImageProps> = ({
     );
   }
 
-  return <img src={imageSrc} alt={alt} {...props} />;
+  return <img src={imageSrc} alt={alt} onLoad={onLoad} {...props} />;
 };
diff --git a/frontend/src/components/gallery/PhotoLightbox.tsx b/frontend/src/components/gallery/PhotoLightbox.tsx
index c6ceb8f6..b9c70d8f 100644
--- a/frontend/src/components/gallery/PhotoLightbox.tsx
+++ b/frontend/src/components/gallery/PhotoLightbox.tsx
@@ -1,6 +1,6 @@
 import React, { useState, useEffect } from 'react';
 import { useDevToolsProtection } from '../../hooks/useDevToolsProtection';
-import { X, ChevronLeft, ChevronRight, Download, ZoomIn, ZoomOut, MessageSquare, Heart, Star } from 'lucide-react';
+import { X, ChevronLeft, ChevronRight, Download, ZoomIn, ZoomOut, MessageSquare, Heart, Star, Loader2 } from 'lucide-react';
 import type { Photo } from '../../types';
 import { useDownloadPhoto } from '../../hooks/useGallery';
 import { AuthenticatedImage } from '../common';
@@ -62,12 +62,18 @@ export const PhotoLightbox: React.FC<PhotoLightboxProps> = ({
   const [savedIdentity, setSavedIdentity] = useState<{ name: string; email: string } | null>(null);
   const [showIdentityModal, setShowIdentityModal] = useState(false);
   const [pendingAction, setPendingAction] = useState<null | { type: 'like' | 'rating'; rating?: number }>(null);
+  const [imageLoaded, setImageLoaded] = useState(false);
 
   useEffect(() => {
     const onResize = () => setIsSmallScreen(window.innerWidth < 640);
     window.addEventListener('resize', onResize);
     return () => window.removeEventListener('resize', onResize);
   }, []);
+
+  // Reset image loaded state when changing photos
+  useEffect(() => {
+    setImageLoaded(false);
+  }, [currentIndex]);
   
   const downloadPhotoMutation = useDownloadPhoto();
   const currentPhoto = photos[currentIndex];
@@ -488,6 +494,13 @@ export const PhotoLightbox: React.FC<PhotoLightboxProps> = ({
           right: isDesktopFeedback ? `${desktopFeedbackWidth}px` : 0,
         }}
       >
+        {/* Loading spinner */}
+        {!imageLoaded && currentPhoto.media_type !== 'video' && (
+          <div className="absolute inset-0 flex items-center justify-center z-10">
+            <Loader2 className="w-12 h-12 text-white animate-spin" />
+          </div>
+        )}
+
         {currentPhoto.media_type === 'video' ? (
           <VideoPlayer
             src={currentPhoto.url}
@@ -505,8 +518,10 @@ export const PhotoLightbox: React.FC<PhotoLightboxProps> = ({
             style={{
               transform: `scale(${zoom}) translate(${dragOffset.x / zoom}px, ${dragOffset.y / zoom}px)`,
               transition: isDragging ? 'none' : 'transform 0.2s',
+              opacity: imageLoaded ? 1 : 0,
             }}
             draggable={false}
+            onLoad={() => setImageLoaded(true)}
             useWatermark={useEnhancedProtection}
             watermarkText={useEnhancedProtection ? `${currentPhoto.filename} - Protected` : undefined}
             isGallery={true}
@@ -524,7 +539,7 @@ export const PhotoLightbox: React.FC<PhotoLightboxProps> = ({
             detectDevTools={protectionLevel === 'enhanced' || protectionLevel === 'maximum'}
             onProtectionViolation={(violationType) => {
               console.warn(`Protection violation in lightbox for photo ${currentPhoto.id}: ${violationType}`);
-            
+
             // Track analytics
             if (typeof window !== 'undefined' && (window as any).umami) {
               (window as any).umami.track('lightbox_protection_violation', {
@@ -534,7 +549,7 @@ export const PhotoLightbox: React.FC<PhotoLightboxProps> = ({
                 zoom
               });
             }
-            
+
             // For maximum protection, close lightbox on violation
             if (protectionLevel === 'maximum' &&
                 ['devtools_detected', 'print_screen_detected', 'canvas_access_blocked'].includes(violationType)) {