diff --git a/docs/api/README.md b/docs/api/README.md
index da84259..5535159 100644
--- a/docs/api/README.md
+++ b/docs/api/README.md
@@ -115,6 +115,7 @@ Generated from `@openapi` annotations in [`src/api/routes/`](../../src/api/route
 | [`routes/category/_id/attributevalue.put.md`](routes/category/_id/attributevalue.put.md) | `PUT /category/{id}/attributevalue` |
 | [`routes/category/delete-image.md`](routes/category/delete-image.md) | `DELETE /category/{id}/image` |
 | [`routes/category/add-image.md`](routes/category/add-image.md) | `POST /category/{id}/image` |
+| [`routes/category/_id/image/generate.md`](routes/category/_id/image/generate.md) | `POST /category/{id}/image/generate` |
 | [`routes/category/_id/property.get.md`](routes/category/_id/property.get.md) | `GET /category/{id}/property` |
 | [`routes/category/_id/property.put.md`](routes/category/_id/property.put.md) | `PUT /category/{id}/property` |
 | [`routes/category/_id/property/_propertyId.md`](routes/category/_id/property/_propertyId.md) | `DELETE /category/{id}/property/{propertyId}` |
@@ -315,7 +316,7 @@ Clients subscribe via [`GET /events`](routes/events.md) (`text/event-stream`). A
 | `attributename` | `POST /attributename`, `PUT /attributename/order`, `DELETE /attributename/{id}`, `PATCH /attributename/{id}`, `DELETE /attributevalue/{id}/image`, `POST /attributevalue/{id}/image` |
 | `brand` | `POST /brand`, `DELETE /brand/{id}`, `PATCH /brand/{id}`, `DELETE /brand/{id}/image`, `POST /brand/{id}/image` |
 | `carrier` | `POST /carrier`, `PUT /carrier/order`, `DELETE /carrier/{id}`, `PATCH /carrier/{id}` |
-| `category` | `POST /category`, `PUT /category/order`, `DELETE /category/{id}`, `PATCH /category/{id}`, `DELETE /category/{id}/image`, `POST /category/{id}/image` |
+| `category` | `POST /category`, `PUT /category/order`, `DELETE /category/{id}`, `PATCH /category/{id}`, `DELETE /category/{id}/image`, `POST /category/{id}/image`, `POST /category/{id}/image/generate` |
 | `delivery` | `DELETE /delivery/{id}/file/{fileId}`, `POST /delivery/{id}/pdf`, `POST /stock/accept` |
 | `labeltemplate` | `POST /labeltemplate`, `DELETE /labeltemplate/{id}`, `PATCH /labeltemplate/{id}`, `PUT /labeltemplate/{id}` |
 | `ledger` | `DELETE /shipment/{id}`, `POST /stock/accept`, `POST /stock/adjust`, `POST /stock/ship` |
diff --git a/docs/api/routes-all.md b/docs/api/routes-all.md
index cc44c99..0c7b943 100644
--- a/docs/api/routes-all.md
+++ b/docs/api/routes-all.md
@@ -1,6 +1,6 @@
 # Dash API Routes Overview (All)
 
-Overview of all 269 API endpoints across all modules.
+Overview of all 270 API endpoints across all modules.
 
 ### Notation
 
@@ -329,6 +329,9 @@ _none_
 #### Add category image — `POST /category/{id}/image`
 - Params: `id: int, image/avif`
 - Returns: `201 { category: { id: int, thumbW: int, thumbH: int, thumbHash: str } }`
+#### Generate category mosaic image from contents — `POST /category/{id}/image/generate`
+- Params: `id: int, body?: { size?: int }`
+- Returns: `200 { category: { id: int, fullHash: str, thumbW: int, thumbH: int, thumbHash: str, size: int, grid: str, articleCount: int } }`
 #### List category properties — `GET /category/{id}/property`
 - Params: `id: int`
 - Returns: `200 { properties: { id: int, propertyId: int, name: str, exclusive: bool, value: str, sort: int, categoryId?: int }[] }`
diff --git a/docs/api/routes.md b/docs/api/routes.md
index 3a4fda6..824e02e 100644
--- a/docs/api/routes.md
+++ b/docs/api/routes.md
@@ -1,6 +1,6 @@
 # Dash API Routes Overview
 
-Overview of all 189 API endpoints across all modules.
+Overview of all 190 API endpoints across all modules.
 
 ### Notation
 
@@ -253,6 +253,9 @@ _none_
 #### Delete category image — `DELETE /category/{id}/image`
 - Params: `id: int`
 - Returns: `200 { category: { id: int, thumbW: int|null, thumbH: int|null, thumbHash: str|null } }`
+#### Generate category mosaic image from contents — `POST /category/{id}/image/generate`
+- Params: `id: int, body?: { size?: int }`
+- Returns: `200 { category: { id: int, fullHash: str, thumbW: int, thumbH: int, thumbHash: str, size: int, grid: str, articleCount: int } }`
 #### List category properties — `GET /category/{id}/property`
 - Params: `id: int`
 - Returns: `200 { properties: { id: int, propertyId: int, name: str, exclusive: bool, value: str, sort: int, categoryId?: int }[] }`
diff --git a/docs/api/routes/category/_id/image/generate.md b/docs/api/routes/category/_id/image/generate.md
new file mode 100644
index 0000000..8e832cc
--- /dev/null
+++ b/docs/api/routes/category/_id/image/generate.md
@@ -0,0 +1,64 @@
+# `POST /category/{id}/image/generate`
+
+Protected. Requires a valid session cookie (`credentials: 'include'`).
+
+Generate category mosaic image from contents
+
+Generates a 2x2, 3x3, or 4x4 mosaic image from the category's and its subcategories'
+articles (grouped by subcategory) and sets it as the new main picture for the category.
+If size is not specified, defaults to 3 (3x3), falling back to 2 (2x2) if fewer than 7 images are available.
+
+
+## Path parameters
+
+| Param | Required | Type | Description |
+|-------|----------|------|-------------|
+| `id` | yes | integer | Category id |
+
+## Body (JSON) — _optional_
+
+| Field | Required | Type | Description |
+|-------|----------|------|-------------|
+| `size` | no | integer | Mosaic grid size (2 for 2x2, 3 for 3x3, 4 for 4x4). Defaults to 3x3 (or 2x2 if < 7 images). |
+
+```json
+{
+  "size": 1
+}
+```
+
+## Signals
+
+On success, emits SSE signal: `category` (see [`GET /events`](../events.md)).
+
+## Response `200`
+
+Mosaic image generated and linked as category main picture
+
+```json
+{
+  "category": {
+    "id": 1,
+    "fullHash": "…",
+    "thumbW": 1,
+    "thumbH": 1,
+    "thumbHash": "…",
+    "size": 1,
+    "grid": "…",
+    "articleCount": 1
+  }
+}
+```
+
+## Errors
+
+| Status | Description |
+|--------|-------------|
+| 400 | Invalid category ID or size — `{"error":"…"}` |
+| 401 | Unauthorized — `{"error":"…"}` |
+| 403 | Not authorized — `{"error":"…"}` |
+| 404 | Category not found or no article images found — `{"error":"…"}` |
+
+---
+
+_Generated from `@openapi` JSDoc. Do not edit by hand — run `npm run docs:api`._
diff --git a/src/api/routes/category.js b/src/api/routes/category.js
index bbb9ba6..3b78bee 100644
--- a/src/api/routes/category.js
+++ b/src/api/routes/category.js
@@ -907,4 +907,122 @@ export function register(app, basePath = '') {
     });
 
     // #endregion
+
+    /**
+     * @openapi
+     * /category/{id}/image/generate:
+     *   post:
+     *     tags: [Category]
+     *     summary: Generate category mosaic image from contents
+     *     description: |
+     *       Generates a 2x2, 3x3, or 4x4 mosaic image from the category's and its subcategories'
+     *       articles (grouped by subcategory) and sets it as the new main picture for the category.
+     *       If size is not specified, defaults to 3 (3x3), falling back to 2 (2x2) if fewer than 7 images are available.
+     *     security:
+     *       - cookieAuth: []
+     *     x-signals: [category]
+     *     parameters:
+     *       - in: path
+     *         name: id
+     *         required: true
+     *         schema:
+     *           type: integer
+     *         description: Category id
+     *     requestBody:
+     *       required: false
+     *       content:
+     *         application/json:
+     *           schema:
+     *             type: object
+     *             properties:
+     *               size:
+     *                 type: integer
+     *                 enum: [2, 3, 4]
+     *                 description: Mosaic grid size (2 for 2x2, 3 for 3x3, 4 for 4x4). Defaults to 3x3 (or 2x2 if < 7 images).
+     *     responses:
+     *       200:
+     *         description: Mosaic image generated and linked as category main picture
+     *         content:
+     *           application/json:
+     *             schema:
+     *               type: object
+     *               properties:
+     *                 category:
+     *                   type: object
+     *                   properties:
+     *                     id:
+     *                       type: integer
+     *                     fullHash:
+     *                       type: string
+     *                     thumbW:
+     *                       type: integer
+     *                     thumbH:
+     *                       type: integer
+     *                     thumbHash:
+     *                       type: string
+     *                     size:
+     *                       type: integer
+     *                     grid:
+     *                       type: string
+     *                     articleCount:
+     *                       type: integer
+     *       400:
+     *         description: Invalid category ID or size
+     *         content:
+     *           application/json:
+     *             schema:
+     *               $ref: '#/components/schemas/Error'
+     *       401:
+     *         description: Unauthorized
+     *         content:
+     *           application/json:
+     *             schema:
+     *               $ref: '#/components/schemas/Error'
+     *       403:
+     *         description: Not authorized
+     *         content:
+     *           application/json:
+     *             schema:
+     *               $ref: '#/components/schemas/Error'
+     *       404:
+     *         description: Category not found or no article images found
+     *         content:
+     *           application/json:
+     *             schema:
+     *               $ref: '#/components/schemas/Error'
+     */
+    // #region POST /category/:id/image/generate
+
+    app.post(
+        `${basePath}/category/:id/image/generate`,
+        express.json(),
+        async (req, res) => {
+            const parsed = parsePositiveInt(req.params.id, 'id');
+            if (parsed.error) {
+                return res.status(400).json({ error: parsed.error });
+            }
+
+            const rawSize = req.body?.size;
+            let size = undefined;
+            if (rawSize !== undefined && rawSize !== null && rawSize !== '') {
+                size = Number(rawSize);
+                if (![2, 3, 4].includes(size)) {
+                    return res.status(400).json({ error: 'Invalid size, must be 2, 3, or 4' });
+                }
+            }
+
+            try {
+                const category = await db.generateImage(req.user.id, parsed.id, { size });
+                emitCategorySignal(req);
+                res.status(200).json({ category });
+            } catch (error) {
+                const status = categoryErrorStatus(error);
+                if (status === 500) console.error('Generate category image failed:', error);
+                res.status(status).json({ error: error.message });
+            }
+        },
+    );
+
+    // #endregion
 }
+
diff --git a/src/db/category.js b/src/db/category.js
index bf20865..779501e 100644
--- a/src/db/category.js
+++ b/src/db/category.js
@@ -44,3 +44,9 @@ export async function deleteImage(googleAuthId, categoryId) {
     const store = await getStore();
     return store.category.deleteImage(googleAuthId, categoryId);
 }
+
+export async function generateImage(googleAuthId, categoryId, options) {
+    const store = await getStore();
+    return store.category.generateImage(googleAuthId, categoryId, options);
+}
+