diff --git a/apps/api-service/src/routes/v1/images.ts b/apps/api-service/src/routes/v1/images.ts
index f107789..9660e90 100644
--- a/apps/api-service/src/routes/v1/images.ts
+++ b/apps/api-service/src/routes/v1/images.ts
@@ -13,7 +13,7 @@ import { validateAndNormalizePagination } from '@/utils/validators';
 import { buildPaginatedResponse } from '@/utils/helpers';
 import { toImageResponse } from '@/types/responses';
 import { db } from '@/db';
-import { flows } from '@banatie/database';
+import { flows, type Image } from '@banatie/database';
 import { eq } from 'drizzle-orm';
 import type {
   UploadImageResponse,
@@ -704,13 +704,14 @@ imagesRouter.put(
 );
 
 /**
- * Assign a project-scoped alias to an image
+ * Assign or remove a project-scoped alias from an image
  *
- * Sets or updates the project-scoped alias for an image:
- * - Alias must start with @ symbol
+ * Sets, updates, or removes the project-scoped alias for an image:
+ * - Alias must start with @ symbol (when assigning)
  * - Must be unique within the project
  * - Replaces existing alias if image already has one
  * - Used for alias resolution in generations and CDN access
+ * - Set alias to null to remove existing alias
  *
  * This is a dedicated endpoint introduced in Section 6.1 to separate
  * alias assignment from general metadata updates.
@@ -722,24 +723,30 @@ imagesRouter.put(
  * @param {string} req.params.id_or_alias - Image ID (UUID) or alias (@-prefixed)
  * @param {string} [req.query.flowId] - Flow ID for flow-scoped alias resolution
  * @param {object} req.body - Request body
- * @param {string} req.body.alias - Project-scoped alias (e.g., "@hero-bg")
+ * @param {string|null} req.body.alias - Project-scoped alias (e.g., "@hero-bg") or null to remove
  *
- * @returns {UpdateImageResponse} 200 - Updated image with new alias
+ * @returns {UpdateImageResponse} 200 - Updated image with new/removed alias
  * @returns {object} 404 - Image not found or access denied
- * @returns {object} 400 - Missing or invalid alias
+ * @returns {object} 400 - Invalid alias format
  * @returns {object} 401 - Missing or invalid API key
  * @returns {object} 409 - Alias already exists
  *
  * @throws {Error} IMAGE_NOT_FOUND - Image does not exist
- * @throws {Error} VALIDATION_ERROR - Alias is required
+ * @throws {Error} VALIDATION_ERROR - Invalid alias format
  * @throws {Error} ALIAS_CONFLICT - Alias already assigned to another image
  *
- * @example UUID identifier
+ * @example Assign alias
  * PUT /api/v1/images/550e8400-e29b-41d4-a716-446655440000/alias
  * {
  *   "alias": "@hero-background"
  * }
  *
+ * @example Remove alias
+ * PUT /api/v1/images/550e8400-e29b-41d4-a716-446655440000/alias
+ * {
+ *   "alias": null
+ * }
+ *
  * @example Project-scoped alias identifier
  * PUT /api/v1/images/@old-hero/alias
  * {
@@ -762,11 +769,12 @@ imagesRouter.put(
     const { flowId } = req.query;
     const { alias } = req.body;
 
-    if (!alias || typeof alias !== 'string') {
+    // Validate: alias must be null (to remove) or a non-empty string
+    if (alias !== null && (typeof alias !== 'string' || alias.trim() === '')) {
       res.status(400).json({
         success: false,
         error: {
-          message: 'Alias is required and must be a string',
+          message: 'Alias must be null (to remove) or a non-empty string',
           code: 'VALIDATION_ERROR',
         },
       });
@@ -815,7 +823,16 @@ imagesRouter.put(
       return;
     }
 
-    const updated = await service.assignProjectAlias(imageId, alias);
+    // Either remove alias (null) or assign new one (override behavior per Section 5.2)
+    let updated: Image;
+    if (alias === null) {
+      // Remove alias
+      updated = await service.update(imageId, { alias: null });
+    } else {
+      // Reassign alias (clears from any existing image, then assigns to this one)
+      await service.reassignProjectAlias(alias, imageId, image.projectId);
+      updated = (await service.getById(imageId))!;
+    }
 
     res.json({
       success: true,
diff --git a/apps/api-service/src/services/core/ImageService.ts b/apps/api-service/src/services/core/ImageService.ts
index f46ee08..76e6542 100644
--- a/apps/api-service/src/services/core/ImageService.ts
+++ b/apps/api-service/src/services/core/ImageService.ts
@@ -89,7 +89,7 @@ export class ImageService {
   async update(
     id: string,
     updates: {
-      alias?: string;
+      alias?: string | null;
       focalPoint?: { x: number; y: number };
       meta?: Record<string, unknown>;
     }
diff --git a/tests/api/utils.ts b/tests/api/utils.ts
index 4375da7..d604ea2 100644
--- a/tests/api/utils.ts
+++ b/tests/api/utils.ts
@@ -139,11 +139,21 @@ export async function uploadFile(
 ): Promise<any> {
   const formData = new FormData();
 
-  // Read file
+  // Read file and detect MIME type from extension
   const fs = await import('fs/promises');
+  const path = await import('path');
   const fileBuffer = await fs.readFile(filepath);
-  const blob = new Blob([fileBuffer]);
-  formData.append('file', blob, 'test-image.png');
+  const ext = path.extname(filepath).toLowerCase();
+  const mimeTypes: Record<string, string> = {
+    '.png': 'image/png',
+    '.jpg': 'image/jpeg',
+    '.jpeg': 'image/jpeg',
+    '.webp': 'image/webp',
+  };
+  const mimeType = mimeTypes[ext] || 'application/octet-stream';
+  const filename = path.basename(filepath);
+  const blob = new Blob([fileBuffer], { type: mimeType });
+  formData.append('file', blob, filename);
 
   // Add other fields
   for (const [key, value] of Object.entries(fields)) {