Update app.py

app.py

@@ -23,6 +23,7 @@ from detectron2.engine import DefaultPredictor
 from detectron2.config import get_cfg
 from detectron2.utils.visualizer import Visualizer
 from detectron2.data import MetadataCatalog, DatasetCatalog
+import cv2
 
 # ????
 setup_logger()