diff --git a/app/src/components/auth/AuthBackground.tsx b/app/src/components/auth/AuthBackground.tsx
index 86c6d31..5a6617f 100644
--- a/app/src/components/auth/AuthBackground.tsx
+++ b/app/src/components/auth/AuthBackground.tsx
@@ -1,4 +1,4 @@
-import { BACKGROUND_IMAGES } from '../../lib/backgrounds';
+import { BACKGROUND_SCENES } from '../../lib/backgrounds';
 import { useBackgroundCrossfade } from '../../hooks/useBackgroundCrossfade';
 
 export function AuthBackground() {
@@ -6,15 +6,43 @@ export function AuthBackground() {
 
   return (
     <div className="absolute inset-0 overflow-hidden bg-[#07080c]">
-      {BACKGROUND_IMAGES.map((bg, i) => (
+      {BACKGROUND_SCENES.map((scene, i) => (
         <div
-          key={bg}
-          className="absolute inset-0 scale-105 bg-cover bg-center transition-opacity duration-[2000ms] ease-in-out"
-          style={{ background: bg, opacity: i === activeIndex ? 1 : 0 }}
-        />
+          key={scene.id}
+          className="absolute inset-0 transition-opacity duration-[2400ms] ease-in-out"
+          style={{ opacity: i === activeIndex ? 1 : 0 }}
+        >
+          {scene.blobs.map((blob, bi) => (
+            <div
+              key={bi}
+              className="tc-drift absolute rounded-full blur-[90px]"
+              style={{
+                top: blob.top,
+                left: blob.left,
+                width: blob.size,
+                height: blob.size,
+                background: blob.color,
+                animationDelay: `${bi * -7}s`,
+              }}
+            />
+          ))}
+        </div>
       ))}
-      <div className="absolute inset-0 bg-[linear-gradient(100deg,rgba(6,7,11,0.92)_0%,rgba(6,7,11,0.62)_46%,rgba(6,7,11,0.28)_100%)]" />
-      <div className="absolute -right-[8%] -top-[18%] h-[52vw] w-[52vw] rounded-full bg-[radial-gradient(circle,rgba(91,140,255,0.26)_0%,transparent_66%)] blur-[10px]" />
+
+      {/* Grain léger : casse l'effet "dégradé plat", donne une texture
+          plus organique - technique courante sur les fonds génératifs. */}
+      <svg className="absolute inset-0 h-full w-full opacity-[0.05] mix-blend-overlay" aria-hidden="true">
+        <filter id="tc-grain">
+          <feTurbulence type="fractalNoise" baseFrequency="0.85" numOctaves="2" stitchTiles="stitch" />
+        </filter>
+        <rect width="100%" height="100%" filter="url(#tc-grain)" />
+      </svg>
+
+      {/* Scrim en deux passes : un voile uniforme (garantit le contraste du
+          texte quelle que soit la position des taches de couleur) plus un
+          dégradé directionnel plus marqué côté texte. */}
+      <div className="absolute inset-0 bg-[#07080c]/48" />
+      <div className="absolute inset-0 bg-[linear-gradient(100deg,rgba(6,7,11,0.74)_0%,rgba(6,7,11,0.44)_46%,rgba(6,7,11,0.22)_100%)]" />
     </div>
   );
 }
diff --git a/app/src/hooks/useBackgroundCrossfade.ts b/app/src/hooks/useBackgroundCrossfade.ts
index 8d16b6f..ba17ca6 100644
--- a/app/src/hooks/useBackgroundCrossfade.ts
+++ b/app/src/hooks/useBackgroundCrossfade.ts
@@ -1,14 +1,15 @@
 import { useEffect, useState } from 'react';
-import { BACKGROUND_IMAGES } from '../lib/backgrounds';
+import { BACKGROUND_SCENES } from '../lib/backgrounds';
 
-const INTERVAL_MS = 5400;
+const INTERVAL_MS = 8000;
 
 export function useBackgroundCrossfade(): number {
   const [index, setIndex] = useState(0);
 
   useEffect(() => {
+    if (window.matchMedia('(prefers-reduced-motion: reduce)').matches) return;
     const id = window.setInterval(() => {
-      setIndex((i) => (i + 1) % BACKGROUND_IMAGES.length);
+      setIndex((i) => (i + 1) % BACKGROUND_SCENES.length);
     }, INTERVAL_MS);
     return () => window.clearInterval(id);
   }, []);
diff --git a/app/src/index.css b/app/src/index.css
index 3f9cdbd..2effa0e 100644
--- a/app/src/index.css
+++ b/app/src/index.css
@@ -93,6 +93,26 @@ input::placeholder {
   animation: tc-pulse 2.4s ease-in-out infinite;
 }
 
+@keyframes tc-drift {
+  0%,
+  100% {
+    transform: translate(0, 0) scale(1);
+  }
+  50% {
+    transform: translate(3%, -4%) scale(1.06);
+  }
+}
+
+.tc-drift {
+  animation: tc-drift 22s ease-in-out infinite;
+}
+
+@media (prefers-reduced-motion: reduce) {
+  .tc-drift {
+    animation: none;
+  }
+}
+
 .upload-progress-stripes {
   background-image: linear-gradient(
     115deg,
diff --git a/app/src/lib/backgrounds.ts b/app/src/lib/backgrounds.ts
index 501e37b..8d2ff6e 100644
--- a/app/src/lib/backgrounds.ts
+++ b/app/src/lib/backgrounds.ts
@@ -1,10 +1,49 @@
 /**
- * Auth-screen background layers. Replace each entry with
- * `url('/assets/bg-1.jpg') center/cover no-repeat` for real photography —
- * the crossfade logic in useBackgroundCrossfade doesn't change.
+ * Scènes du diaporama de fond de l'écran de connexion : de l'art génératif
+ * (pas de photo tierce, pour rester libre de droits) - deux à trois taches
+ * de couleur douces, floutées, qui dérivent lentement (voir `.tc-drift`
+ * dans index.css) et s'enchaînent en fondu. Palette "zen" volontairement
+ * sourde : jamais de couleur saturée à pleine opacité.
  */
-export const BACKGROUND_IMAGES: string[] = [
-  'radial-gradient(120% 95% at 22% 12%, #2b3340 0%, #121620 55%, #070910 100%)',
-  'radial-gradient(120% 95% at 78% 18%, #2f2b3f 0%, #16131f 55%, #08070d 100%)',
-  'radial-gradient(130% 100% at 45% 85%, #1f3340 0%, #0f161c 55%, #070a0d 100%)',
+export interface BackgroundBlob {
+  color: string;
+  top: string;
+  left: string;
+  size: string;
+}
+
+export interface BackgroundScene {
+  id: string;
+  blobs: BackgroundBlob[];
+}
+
+export const BACKGROUND_SCENES: BackgroundScene[] = [
+  {
+    id: 'aube',
+    blobs: [
+      { color: 'rgba(123,148,255,0.42)', top: '-12%', left: '58%', size: '56vw' },
+      { color: 'rgba(255,168,140,0.24)', top: '52%', left: '2%', size: '44vw' },
+    ],
+  },
+  {
+    id: 'nuit',
+    blobs: [
+      { color: 'rgba(91,102,255,0.38)', top: '-16%', left: '72%', size: '60vw' },
+      { color: 'rgba(124,92,255,0.3)', top: '58%', left: '12%', size: '50vw' },
+    ],
+  },
+  {
+    id: 'foret',
+    blobs: [
+      { color: 'rgba(94,214,170,0.22)', top: '8%', left: '76%', size: '48vw' },
+      { color: 'rgba(53,124,132,0.38)', top: '62%', left: '6%', size: '54vw' },
+    ],
+  },
+  {
+    id: 'braise',
+    blobs: [
+      { color: 'rgba(255,186,128,0.26)', top: '-6%', left: '18%', size: '50vw' },
+      { color: 'rgba(179,111,255,0.3)', top: '54%', left: '68%', size: '54vw' },
+    ],
+  },
 ];