title: error: (-215) !empty() in function detectMultiScale
body: <p>I'm trying to learn cv2 in python 2.7, but when I run my code, in the specific part of it:</p>
  
  <pre><code>face_cascade = cv2.CascadeClassifier('haarcascade_frontalface_default.xml')
   eye_cascade = cv2.CascadeClassifier('haarcascade_eye.xml')
  
  
  img = cv2.imread('2015-05-27-191152.jpg')
  gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
  
  faces = face_cascade.detectMultiScale(gray, 1.3, 5)
  for (x,y,w,h) in faces:
      img = cv2.rectangle(img,(x,y),(x+w,y+h),(255,0,0),2)
  </code></pre>
  
  <p>it returns this:</p>
  
  <pre><code>File "face_detection.py", line 11, in &lt;module&gt;
      faces = face_cascade.detectMultiScale(gray, 1.3, 5)
  cv2.error: /home/arthurckl/Desktop/opencv-3.0.0-rc1/modules/objdetect/src/cascadedetect.cpp:1595: error: (-215) !empty() in function detectMultiScale
  </code></pre>
  
  <p>I tried to search the answer here but the best i could find is that I must be loading the face_cascade the wrong way... Any help?</p>