update requirements and fix cv2 import in dockerfile

backend/Dockerfile

@@ -13,6 +13,9 @@ RUN pip install -r requirements.txt
 
 FROM python:3.9 AS runtime
 
+RUN apt-get update
+RUN apt-get install ffmpeg libsm6 libxext6  -y
+
 EXPOSE 80
 ENV PATH="/venv/bin:$PATH"