diff --git a/src/nrtk_explorer/app/transforms.py b/src/nrtk_explorer/app/transforms.py
index d1324159..72e911c9 100644
--- a/src/nrtk_explorer/app/transforms.py
+++ b/src/nrtk_explorer/app/transforms.py
@@ -204,7 +204,7 @@ def compute_annotations(self, ids):
         if len(ids) == 0:
             return
 
-        predictions = self.detector.eval(paths=ids, content=self.context.image_objects)
+        predictions = self.detector.eval(image_ids=ids, content=self.context.image_objects)
 
         for id_, annotations in predictions:
             image_annotations = self.context["annotations"].setdefault(id_, [])
diff --git a/src/nrtk_explorer/library/nrtk_transforms.py b/src/nrtk_explorer/library/nrtk_transforms.py
index be891c61..d064cb8c 100644
--- a/src/nrtk_explorer/library/nrtk_transforms.py
+++ b/src/nrtk_explorer/library/nrtk_transforms.py
@@ -1,4 +1,4 @@
-from typing import Any, Dict
+from typing import Any, Dict, Union
 
 import numpy as np
 import logging
@@ -25,7 +25,7 @@ def nrtk_transforms_available():
 
 
 class NrtkGaussianBlurTransform(ImageTransform):
-    def __init__(self, perturber=None):
+    def __init__(self, perturber: Union[GaussianBlurPerturber, None] = None):
         if perturber is None:
             perturber = GaussianBlurPerturber()
 
@@ -155,7 +155,7 @@ def createSampleSensorAndScenario():
 
 
 class NrtkPybsmTransform(ImageTransform):
-    def __init__(self, perturber=None):
+    def __init__(self, perturber: Union[PybsmPerturber, None] = None):
         if perturber is None:
             sensor, scenario = createSampleSensorAndScenario()
             perturber = PybsmPerturber(sensor=sensor, scenario=scenario)
diff --git a/src/nrtk_explorer/library/object_detector.py b/src/nrtk_explorer/library/object_detector.py
index 945726bd..72eaccae 100644
--- a/src/nrtk_explorer/library/object_detector.py
+++ b/src/nrtk_explorer/library/object_detector.py
@@ -8,7 +8,11 @@
 
 from nrtk_explorer.library import images_manager
 
-Annotations = list[list[tuple[str, dict]]]
+Annotation = dict  # in COCO format
+Annotations = list[Annotation]
+ImageId = str
+AnnotatedImage = tuple[ImageId, Annotations]
+AnnotatedImages = list[AnnotatedImage]
 
 
 class ObjectDetector:
@@ -59,19 +63,16 @@ def pipeline(self, model_name: str):
 
     def eval(
         self,
-        paths: list[str],
+        image_ids: list[str],
         content: Optional[dict] = None,
         batch_size: int = 32,
-    ) -> Annotations:
-        """Compute object recognition, return it in a list of tuples in the form of [(path, annotations dict in COCO Format)]"""
-        if len(paths) == 0:
-            return []
-
+    ) -> AnnotatedImages:
+        """Compute object recognition. Returns Annotations grouped by input image paths."""
         images: dict = {}
 
         # Some models require all the images in a batch to be the same size,
         # otherwise crash or UB.
-        for path in paths:
+        for path in image_ids:
             img = None
             if content and path in content:
                 img = content[path]
@@ -93,12 +94,12 @@ def eval(
             for group in images.values()
         ]
         # Flatten the list of predictions
-        predictions = reduce(operator.iadd, predictions)  # type: ignore
-
-        output = list()
-        for path in paths:
-            for prediction in predictions:
-                if prediction[0] == path:
-                    output.append(prediction)
-
-        return output
+        predictions = reduce(operator.iadd, predictions, [])
+
+        # order output by paths order
+        find_prediction = lambda id: next(
+            prediction for prediction in predictions if prediction[0] == id
+        )
+        output = [find_prediction(path) for path in image_ids]
+        # mypy wrongly thinks output's type is list[list[tuple[str, dict]]]
+        return output  # type: ignore
diff --git a/tests/test_object_detector.py b/tests/test_object_detector.py
index 72cfb238..ab2e30f7 100644
--- a/tests/test_object_detector.py
+++ b/tests/test_object_detector.py
@@ -18,7 +18,7 @@ def test_detector_small():
     ds = json.load(open(DATASET))
     sample = [f"{DATASET_PATH}/{img['file_name']}" for img in ds["images"]][:15]
     detector = object_detector.ObjectDetector(model_name="hustvl/yolos-tiny")
-    img = detector.eval(paths=sample)
+    img = detector.eval(image_ids=sample)
     assert len(img) == 15
 
 
@@ -26,7 +26,7 @@ def test_nrkt_scorer():
     ds = json.load(open(DATASET))
     sample = [f"{DATASET_PATH}/{img['file_name']}" for img in ds["images"]]
     detector = object_detector.ObjectDetector(model_name="facebook/detr-resnet-50")
-    predictions = detector.eval(paths=sample)
+    predictions = detector.eval(image_ids=sample)
 
     dataset_annotations = dict()
     for annotation in ds["annotations"]: