thumbnail issue

backend/app.py

@@ -75,9 +75,10 @@ async def return_thumbnails():
     thumbnails = []
     for item in data:
         pil_image = convert_to_pil(item['image'])
-        # resize into 200x200 thumbnails
-        pil_image.thumbnail((256, 256))
-        thumbnails.append(pil_image)
+        # make a copy
+        thumb_img = pil_image.copy()
+        thumb_img.thumbnail((256, 256))
+        thumbnails.append(thumb_img)
     return thumbnails
 
 def rgb_to_hex(rgb):