Demo Failure : Cannot detect face .Why?

edit

This is the result:

You can see there is no detect rectangle. Where is wrong?

Thanks!

Below is my codes:

import numpy as np
import cv2
face_cascade = cv2.CascadeClassifier('haarcascade_frontalface_default.xml')
eye_cascade = cv2.CascadeClassifier('haarcascade_eye.xml')
img = cv2.imread('./nbaplayer/203500.png')
print img.shape
print img.size
gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
hsv = cv2.cvtColor(img, cv2.COLOR_BGR2HSV)
#print gray.shape
#print gray.size
#cv2.imshow('img1',gray)
cv2.imshow('hsv',hsv)
faces = face_cascade.detectMultiScale(gray,2,1)
print faces
for (x,y,w,h) in faces:
 img = 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.rectangle(img,(38,0),(23,128),(255,255,255),3)
cv2.imshow('img',img)
cv2.waitKey(0)
cv2.destroyAllWindows()