diff --git a/docs/stories/3.6.optimisation-images.md b/docs/stories/3.6.optimisation-images.md
index 3c5bbfa..8a14731 100644
--- a/docs/stories/3.6.optimisation-images.md
+++ b/docs/stories/3.6.optimisation-images.md
@@ -2,7 +2,7 @@
 
 ## Status
 
-Ready for Dev
+In Progress
 
 ## Story
 
@@ -21,28 +21,28 @@ Ready for Dev
 
 ## Tasks / Subtasks
 
-- [] **Task 1 : Organiser le dossier images** (AC: 1)
-  - [] Créer `assets/img/projects/`
-  - [] Définir la convention de nommage : `{slug}-{type}.{ext}`
-  - [] Exemple : `ecommerce-xyz-thumb.webp`, `ecommerce-xyz-screen-1.webp`
+- [x] **Task 1 : Organiser le dossier images** (AC: 1)
+  - [x] Créer `assets/img/projects/`
+  - [x] Définir la convention de nommage : `{slug}-{type}.{ext}`
+  - [x] Exemple : `ecommerce-xyz-thumb.webp`, `ecommerce-xyz-screen-1.webp`
 
-- [] **Task 2 : Implémenter le lazy loading** (AC: 2)
-  - [] Ajouter `loading="lazy"` sur toutes les images projets
-  - [] Image principale above-the-fold sans lazy loading (false)
+- [x] **Task 2 : Implémenter le lazy loading** (AC: 2)
+  - [x] Ajouter `loading="lazy"` sur toutes les images projets
+  - [x] Image principale above-the-fold sans lazy loading (false)
 
-- [] **Task 3 : Ajouter les dimensions explicites** (AC: 3)
-  - [] Définir les tailles standards : thumbnail (400x225), screenshot (800x450), hero (1200x675)
-  - [] Ajouter `width` et `height` sur toutes les `<img>`
+- [x] **Task 3 : Ajouter les dimensions explicites** (AC: 3)
+  - [x] Définir les tailles standards : thumbnail (400x225), screenshot (800x450), hero (1200x675)
+  - [x] Ajouter `width` et `height` sur toutes les `<img>`
 
-- [] **Task 4 : Implémenter WebP avec fallback** (AC: 4)
-  - [] Utiliser `<picture>` avec `<source type="image/webp">`
-  - [] Fallback vers JPG
+- [x] **Task 4 : Implémenter WebP avec fallback** (AC: 4)
+  - [x] Utiliser `<picture>` avec `<source type="image/webp">`
+  - [x] Fallback vers JPG
 
-- [] **Task 5 : Documenter les tailles recommandées** (AC: 5)
-  - [] Thumbnails : 400x225, qualité 80%
-  - [] Screenshots : 800x450, qualité 85%
-  - [] Hero : 1200x675, qualité 85%
-  - [] Documentation dans Dev Notes
+- [x] **Task 5 : Documenter les tailles recommandées** (AC: 5)
+  - [x] Thumbnails : 400x225, qualité 80%
+  - [x] Screenshots : 800x450, qualité 85%
+  - [x] Hero : 1200x675, qualité 85%
+  - [x] Documentation dans Dev Notes
 
 - [ ] **Task 6 : Tester les performances** (AC: 6)
   - [ ] Audit Lighthouse sur la page projets (requiert images réelles)
@@ -168,7 +168,7 @@ done
 ## Dev Agent Record
 
 ### Agent Model Used
-Claude Opus 4.5 (claude-opus-4-5-20251101)
+GPT-5 Codex
 
 ### File List
 | File | Action | Description |
@@ -176,6 +176,8 @@ Claude Opus 4.5 (claude-opus-4-5-20251101)
 | `includes/functions.php` | Modified | Ajout fonction projectImage() |
 | `templates/project-card.php` | Modified | Utilise projectImage() |
 | `pages/project-single.php` | Modified | Utilise projectImage() pour hero et galerie |
+| `tests/images.test.php` | Created | Tests helper image |
+| `tests/run.ps1` | Modified | Ajout tests image |
 
 ### Completion Notes
 - Fonction `projectImage()` créée avec support `<picture>` WebP + fallback JPG
@@ -183,14 +185,15 @@ Claude Opus 4.5 (claude-opus-4-5-20251101)
 - Lazy loading activé par défaut, désactivé pour images above-the-fold
 - Fallback onerror vers default-project.svg
 - Templates mis à jour: project-card.php, project-single.php
-- Task 6 (Lighthouse) non testable sans images réelles
+- Tests: `powershell -ExecutionPolicy Bypass -File tests/run.ps1`
+- Task 6 (Lighthouse) à faire quand images réelles dispo
 
 ### Debug Log References
-Aucun problème rencontré.
+Aucun problème bloquant.
 
 ## Change Log
 
 | Date | Version | Description | Author |
 |------|---------|-------------|--------|
 | 2026-01-22 | 0.1 | Création initiale | Sarah (PO) |
-| 2026-01-23 | 1.0 | Implémentation complète | James (Dev) |
+| 2026-02-04 | 1.0 | Implémentation partielle (sans Lighthouse) | Amelia |
diff --git a/includes/functions.php b/includes/functions.php
index 0f75bfd..28c71b4 100644
--- a/includes/functions.php
+++ b/includes/functions.php
@@ -78,4 +78,33 @@ function getAllTechnologies(): array
     }
     sort($technologies);
     return $technologies;
+}
+
+/**
+ * Helper pour afficher une image projet optimisée
+ */
+function projectImage(string $filename, string $alt, int $width, int $height, bool $lazy = true): string
+{
+    $webp = $filename;
+    $fallback = str_replace('.webp', '.jpg', $filename);
+    $lazyAttr = $lazy ? 'loading="lazy"' : '';
+
+    $altEsc = htmlspecialchars($alt, ENT_QUOTES, 'UTF-8');
+    $webpEsc = htmlspecialchars($webp, ENT_QUOTES, 'UTF-8');
+    $fallbackEsc = htmlspecialchars($fallback, ENT_QUOTES, 'UTF-8');
+
+    return <<<HTML
+<picture>
+    <source srcset="/assets/img/projects/{$webpEsc}" type="image/webp">
+    <img
+        src="/assets/img/projects/{$fallbackEsc}"
+        alt="{$altEsc}"
+        width="{$width}"
+        height="{$height}"
+        {$lazyAttr}
+        class="w-full h-full object-cover"
+        onerror="this.onerror=null;this.src='/assets/img/projects/default-project.svg';"
+    >
+</picture>
+HTML;
 }
\ No newline at end of file
diff --git a/pages/project-single.php b/pages/project-single.php
index 8aa7c11..6e682d6 100644
--- a/pages/project-single.php
+++ b/pages/project-single.php
@@ -71,13 +71,13 @@ include_template('navbar', compact('currentPage'));
 
             <?php if (!empty($project['thumbnail'])): ?>
                 <div class="mb-12 rounded-lg overflow-hidden">
-                    <img
-                        src="/assets/img/projects/<?= htmlspecialchars($project['thumbnail'], ENT_QUOTES, 'UTF-8') ?>"
-                        alt="<?= htmlspecialchars($project['title'], ENT_QUOTES, 'UTF-8') ?>"
-                        class="w-full"
-                        loading="lazy"
-                        onerror="this.onerror=null;this.src='/assets/img/projects/default-project.svg';"
-                    >
+                    <?= projectImage(
+                        $project['thumbnail'],
+                        $project['title'],
+                        1200,
+                        675,
+                        false
+                    ) ?>
                 </div>
             <?php endif; ?>
 
@@ -115,13 +115,13 @@ include_template('navbar', compact('currentPage'));
                             <h2 class="text-heading mb-4">Captures d'écran</h2>
                             <div class="grid grid-cols-1 sm:grid-cols-2 gap-4">
                                 <?php foreach ($project['screenshots'] as $screenshot): ?>
-                                    <img
-                                        src="/assets/img/projects/<?= htmlspecialchars($screenshot, ENT_QUOTES, 'UTF-8') ?>"
-                                        alt="Capture d'écran - <?= htmlspecialchars($project['title'], ENT_QUOTES, 'UTF-8') ?>"
-                                        class="rounded-lg"
-                                        loading="lazy"
-                                        onerror="this.onerror=null;this.src='/assets/img/projects/default-project.svg';"
-                                    >
+                                    <?= projectImage(
+                                        $screenshot,
+                                        "Capture d'écran - {$project['title']}",
+                                        800,
+                                        450,
+                                        true
+                                    ) ?>
                                 <?php endforeach; ?>
                             </div>
                         </section>
diff --git a/templates/project-card.php b/templates/project-card.php
index e343c2d..3b7475e 100644
--- a/templates/project-card.php
+++ b/templates/project-card.php
@@ -6,7 +6,7 @@
 
 $title = $project['title'] ?? 'Sans titre';
 $slug = $project['slug'] ?? '#';
-$thumbnail = $project['thumbnail'] ?? 'default-project.svg';
+$thumbnail = $project['thumbnail'] ?? 'default-project.webp';
 $technologies = $project['technologies'] ?? [];
 $maxTechs = 4;
 ?>
@@ -14,21 +14,13 @@ $maxTechs = 4;
 <article class="card-interactive group">
     <a href="/projet/<?= htmlspecialchars($slug, ENT_QUOTES, 'UTF-8') ?>" class="block">
         <div class="aspect-thumbnail overflow-hidden">
-            <picture>
-                <source
-                    srcset="/assets/img/projects/<?= htmlspecialchars($thumbnail, ENT_QUOTES, 'UTF-8') ?>"
-                    type="image/webp"
-                >
-                <img
-                    src="/assets/img/projects/<?= htmlspecialchars(str_replace('.webp', '.jpg', $thumbnail), ENT_QUOTES, 'UTF-8') ?>"
-                    alt="Aperçu du projet <?= htmlspecialchars($title, ENT_QUOTES, 'UTF-8') ?>"
-                    width="400"
-                    height="225"
-                    loading="lazy"
-                    class="w-full h-full object-cover transition-transform duration-300 group-hover:scale-105"
-                    onerror="this.onerror=null;this.src='/assets/img/projects/default-project.svg';"
-                >
-            </picture>
+            <?= projectImage(
+                $thumbnail,
+                "Aperçu du projet {$title}",
+                400,
+                225,
+                true
+            ) ?>
         </div>
 
         <div class="card-body">
diff --git a/tests/images.test.php b/tests/images.test.php
new file mode 100644
index 0000000..1169883
--- /dev/null
+++ b/tests/images.test.php
@@ -0,0 +1,20 @@
+<?php
+require_once __DIR__ . '/../includes/functions.php';
+
+function assertTrue($cond, $msg) {
+    if (!$cond) {
+        fwrite(STDERR, $msg . PHP_EOL);
+        exit(1);
+    }
+}
+
+$htmlLazy = projectImage('ecommerce-xyz-thumb.webp', 'Test', 400, 225, true);
+assertTrue(strpos($htmlLazy, 'loading="lazy"') !== false, 'lazy attr missing');
+assertTrue(strpos($htmlLazy, 'type="image/webp"') !== false, 'webp source missing');
+assertTrue(strpos($htmlLazy, 'width="400"') !== false, 'width missing');
+assertTrue(strpos($htmlLazy, 'height="225"') !== false, 'height missing');
+
+$htmlNoLazy = projectImage('ecommerce-xyz-thumb.webp', 'Test', 400, 225, false);
+assertTrue(strpos($htmlNoLazy, 'loading="lazy"') === false, 'lazy should be absent');
+
+fwrite(STDOUT, "OK\n");
\ No newline at end of file
diff --git a/tests/run.ps1 b/tests/run.ps1
index f4304b9..67a67c1 100644
--- a/tests/run.ps1
+++ b/tests/run.ps1
@@ -14,4 +14,5 @@ php (Join-Path $here 'router.test.php')
 php (Join-Path $here 'projects-list.test.php')
 php (Join-Path $here 'project-single.test.php')
 php (Join-Path $here 'projects-secondary.test.php')
+php (Join-Path $here 'images.test.php')
 'OK'
\ No newline at end of file