title: How do I set ROIs in OpenCV for face then mouth detection in video feeds?
body: <p>We are using OpenCV for our project, and we plan to detect the face, then use that created rectangle as our ROI, then detect the mouth there. How do we set the ROI for videos? We searched how, but could only find answers for still images. We would like to set our ROI to the lower 1/3 or lower half of the detected face. </p>
  
  <p>"haarcascade_mcs_mouth.xml" is used, but the rectangle is placed in the wrong spot. The mouth is detected near the right eyebrow. </p>