title: Haar Cascade classifier does not detect faces in simple frontal pictures
body: <p>Trying to do some simple face detection using opencv + python using Haar Cascade Classifier.</p>
  
  <p>Below code perfectly detects faces in <a href="https://drive.google.com/file/d/0Bxed_8T6OPe4ZVNPZXBrWkJ2bEk/view" rel="nofollow">image1</a>, <a href="https://drive.google.com/file/d/0Bxed_8T6OPe4cFQ2U0JPaThld3c/view" rel="nofollow">image2</a> but fails to detect in <a href="https://drive.google.com/file/d/0Bxed_8T6OPe4Ulpfa3pUOVQxXzA/view" rel="nofollow">image3</a></p>
  
  <p>Kindly help me understand what are the reasons for non-detection of face in <a href="https://drive.google.com/file/d/0Bxed_8T6OPe4Ulpfa3pUOVQxXzA/view" rel="nofollow">image3</a></p>
  
  <pre><code>import numpy as np
  import cv2
  
  face_cascade = cv2.CascadeClassifier('haarcascade_frontalface_default.xml')
  eye_cascade = cv2.CascadeClassifier('haarcascade_eye.xml')
  
  img = cv2.imread('/home/swiftguy/computer-vision/image3.jpg')
  gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
  
  faces = face_cascade.detectMultiScale(gray, 1.3, 3)
  for (x,y,w,h) in faces:
      img2 = cv2.rectangle(img,(x,y),(x+w,y+h),(255,0,0),2)
      roi_gray = gray[y:y+h, x:x+w]
      roi_color = img[y:y+h, x:x+w]
      eyes = eye_cascade.detectMultiScale(roi_gray)
      for (ex,ey,ew,eh) in eyes:
              cv2.rectangle(roi_color,(ex,ey),(ex+ew,ey+eh),(0,255,0),2)
  
  cv2.imshow('img',img)
  cv2.waitKey(0)
  cv2.destroyAllWindows()
  </code></pre>