title: Python face detection error with opencv
body: <p>I try to use python face detection software. But when I launch it i recive this error:</p>
  
  <pre><code>OpenCV Error: Unspecified error (The node does not represent a user object (unknown type?)) in cvRead, file /build/opencv-FWWjHr/opencv-2.4.9.1+dfsg/modules/core/src/persistence.cpp, line 4991
  Traceback (most recent call last):
    File "riconoscimentofacciale.py", line 57, in &lt;module&gt;
      faceCascade = cv.Load("haarcascade_frontalface_default.xml")
  cv2.error: The node does not represent a user object (unknown type?)
  </code></pre>
  
  <p>the source code is this:</p>
  
  <pre><code>#!/usr/bin/python
  
  import cv
  import cv2
  import time
  import Image
  
  def DetectFace(image, faceCascade):
  
      min_size = (20,20)
      image_scale = 2
      haar_scale = 1.1
      min_neighbors = 3
      haar_flags = 0
  
      # Allocate the temporary images
      grayscale = cv.CreateImage((image.width, image.height), 8, 1)
      smallImage = cv.CreateImage(
              (
                  cv.Round(image.width / image_scale),
                  cv.Round(image.height / image_scale)
              ), 8 ,1)
  
      # Convert color input image to grayscale
      cv.CvtColor(image, grayscale, cv.CV_BGR2GRAY)
  
      # Scale input image for faster processing
      cv.Resize(grayscale, smallImage, cv.CV_INTER_LINEAR)
  
      # Equalize the histogram
      cv.EqualizeHist(smallImage, smallImage)
  
      # Detect the faces
      faces = cv.HaarDetectObjects(
              smallImage, faceCascade, cv.CreateMemStorage(0),
              haar_scale, min_neighbors, haar_flags, min_size
          )
  
      # If faces are found
      if faces:
          for ((x, y, w, h), n) in faces:
              # the input to cv.HaarDetectObjects was resized, so scale the
              # bounding box of each face and convert it to two CvPoints
              pt1 = (int(x * image_scale), int(y * image_scale))
              pt2 = (int((x + w) * image_scale), int((y + h) * image_scale))
              cv.Rectangle(image, pt1, pt2, cv.RGB(255, 0, 0), 5, 8, 0)
  
      return image
  
  #----------
  # M A I N
  #----------
  
  capture = cv.CaptureFromCAM(0)
  #capture = cv.CaptureFromFile("test.avi")
  
  faceCascade = cv.Load("haarcascade_frontalface_default.xml")
  #faceCascade = cv.Load("haarcascades/haarcascade_frontalface_alt2.xml")
  #faceCascade = cv.Load("haarcascades/haarcascade_frontalface_alt.xml")
  #faceCascade = cv.Load("haarcascades/haarcascade_frontalface_alt_tree.xml")
  
  while (cv.WaitKey(15)==-1):
      img = cv.QueryFrame(capture)
      image = DetectFace(img, faceCascade)
      cv.ShowImage("face detection test", image)
  
  cv.ReleaseCapture(capture)
  </code></pre>
  
  <p>I have set-up all right, I followed <a href="http://www.lucaamore.com/?p=638" rel="nofollow">guide</a></p>
  
  <p>I download all, install all, create and put the right file/drectory. But still face the error.</p>