diff --git a/face_recognition/comparison.py b/face_recognition/comparison.py
index ca12b28..d326dd1 100644
--- a/face_recognition/comparison.py
+++ b/face_recognition/comparison.py
@@ -606,11 +606,19 @@ def display(image_res, q1, q2, q3, q4, fullscreen, output_dir):
             logger.info("Show frame until %f", override_until)
 
             # save images:
-            name = datetime.datetime.now().isoformat(timespec='seconds')
-            cv2.imwrite(os.path.join(output_dir, f'{name}.png'),override_image)
+            name = datetime.datetime.now().isoformat(timespec='seconds').replace(':','-')
+            filename = os.path.join(output_dir, f'{name}.png')
+            print(f"Save to {filename}")
+            r=cv2.imwrite(filename, override_image)
+            if not r:
+                raise RuntimeError(f"Could not save image {filename}")
+            
             for result in results:
                 result_img =result.draw_detections(include_title = True)
-                cv2.imwrite(os.path.join(output_dir, f'{name}-{result.algorithm}.png'), result_img)
+                filename = os.path.join(output_dir, f'{name}-{result.algorithm}.png')
+                r = cv2.imwrite(filename, result_img)
+                if not r:
+                    raise RuntimeError(f"Could not save image {filename}")