diff --git a/src/app/engine/rasterizers.py b/src/app/engine/rasterizers.py
index f9fc2bb..f056a81 100644
--- a/src/app/engine/rasterizers.py
+++ b/src/app/engine/rasterizers.py
@@ -33,7 +33,7 @@ def rasterize_pdf(self, subfolder_path):
         pdf_source = os.path.join(subfolder_path, "source.pdf")
         images = self.__rasterize(pdf_source, subfolder_path, dpi=self._dpi)
         images = self.__validate_rasterized_images(images, pdf_source, subfolder_path)
-        return images
+        return [i.filename for i in images]
 
     def __rasterize(
         self, pdf_source, subfolder_path, start_page=None, last_page=None, dpi=None
@@ -65,6 +65,7 @@ def __validate_rasterized_images(self, images, pdf_source, subfolder_path):
             if res == ResizeResult.SINGLE_PIXEL:
                 single_pixel_pages.append(idx + 1)
             idx += 1
+            im.close()
 
         if single_pixel_pages:
             return self.__rescale_single_page_default_dpi(
@@ -89,8 +90,8 @@ def __ensure_image_size(self, idx, im: Image):
             logger.info(
                 f"resizing image index {idx} from {w},{h} to {scale_w},{scale_h}"
             )
-            resized = im.resize((scale_w, scale_h), resample=Image.LANCZOS)
-            resized.save(filename)
+            with im.resize((scale_w, scale_h), resample=Image.LANCZOS) as resized:
+                resized.save(filename)
             return ResizeResult.RESIZED
 
         return ResizeResult.NOOP
diff --git a/src/app/engine/s3.py b/src/app/engine/s3.py
index eadcd92..35d1249 100644
--- a/src/app/engine/s3.py
+++ b/src/app/engine/s3.py
@@ -26,7 +26,9 @@ def __build_bucket_base_url(self):
         else:
             return f"https://s3.amazonaws.com/{self._bucket_name}"
 
-    def put_images(self, images, submission_id, composite_id, customer_id, space_id):
+    def put_images(
+        self, image_paths, submission_id, composite_id, customer_id, space_id
+    ):
         s3_uris = []
 
         key_prefix = self.__get_key_prefix(
@@ -36,14 +38,14 @@ def put_images(self, images, submission_id, composite_id, customer_id, space_id)
         with tqdm.tqdm(
             desc=f"[{submission_id}] Upload images to S3",
             unit=" image",
-            total=len(images),
+            total=len(image_paths),
         ) as progress_bar:
             with ThreadPoolExecutor(max_workers=self._upload_threads) as executor:
                 # It's critical that the list of S3 URI's returned by this method is in the
                 # same order as the list of images provided to it. '.map(...)' gives us that,
                 # whilst '.submit(...)' does not.
                 for s3_uri in executor.map(
-                    self.__put_image, repeat(key_prefix), images
+                    self.__put_image, repeat(key_prefix), image_paths
                 ):
                     s3_uris.append(s3_uri)
                     progress_bar.update(1)
@@ -52,8 +54,8 @@ def put_images(self, images, submission_id, composite_id, customer_id, space_id)
     def __get_key_prefix(self, submission_id, composite_id, customer, space):
         return f"{self._object_key_prefix}/{customer}/{space}/{composite_id or submission_id}"
 
-    def __put_image(self, key_prefix, image):
-        object_key = f"{key_prefix}/{os.path.basename(image.filename)}"
-        with open(image.filename, "rb") as file:
+    def __put_image(self, key_prefix, image_path):
+        object_key = f"{key_prefix}/{os.path.basename(image_path)}"
+        with open(image_path, "rb") as file:
             self._client.put_object(Bucket=self._bucket_name, Key=object_key, Body=file)
         return f"{self._bucket_base_url}/{object_key}"
diff --git a/src/app/engine/tasks.py b/src/app/engine/tasks.py
index bca2997..3ae7901 100644
--- a/src/app/engine/tasks.py
+++ b/src/app/engine/tasks.py
@@ -28,8 +28,8 @@ def process_member(args):
     folder_path = None
     try:
         folder_path = __fetch_origin(member, member.json_data["origin"])
-        images = __rasterize_composite(member, folder_path)
-        s3_urls = __push_images_to_dlcs(member, images)
+        image_paths = __rasterize_composite(member, folder_path)
+        s3_urls = __push_images_to_dlcs(member, image_paths)
         dlcs_requests = __build_dlcs_requests(member, s3_urls)
         dlcs_responses = __initiate_dlcs_ingest(member, dlcs_requests, args["auth"])
         return __build_result(member, dlcs_responses)
@@ -49,12 +49,12 @@ def __rasterize_composite(member, pdf_path):
     return pdf_rasterizer.rasterize_pdf(pdf_path)
 
 
-def __push_images_to_dlcs(member, images):
-    __update_status(member, "PUSHING_TO_DLCS", image_count=len(images))
+def __push_images_to_dlcs(member, image_paths):
+    __update_status(member, "PUSHING_TO_DLCS", image_count=len(image_paths))
     composite_id = member.json_data.get("compositeId")
     customer = member.collection.customer
     space = member.json_data["space"]
-    return s3_client.put_images(images, member.id, composite_id, customer, space)
+    return s3_client.put_images(image_paths, member.id, composite_id, customer, space)
 
 
 def __build_dlcs_requests(member, dlcs_uris):