detect faces and show them on separate windows. You give the image path as an argument to that python script and see the magic.

face_detection.py

from __future__ import division
import cv2
import cv2.cv as cv
import sys
import pdb

def detect(img, cascade):
        rects = cascade.detectMultiScale(img, scaleFactor=1.1, minNeighbors=3, minSize=(10, 10), flags = cv.CV_HAAR_SCALE_IMAGE)
        if len(rects) == 0:
                return []
        rects[:,2:] += rects[:,:2]
        return rects

def draw_rects(img, rects, color):
        for x1, y1, x2, y2 in rects:
                cv2.rectangle(img, (x1, y1), (x2, y2), color, 2)

if __name__ == '__main__':
        if len(sys.argv) != 2:                                         ## Check for error in usage syntax
                print "Usage : python faces.py <image_file>"

        else:
                img = cv2.imread(sys.argv[1],cv2.CV_LOAD_IMAGE_COLOR)  ## Read image file
                img_x = img.shape[0]
                img_y = img.shape[1]

                print img_x
                print img_y
                img_ratio = img_x / img_y

                if img_x > 512 :
                    #newx,newy = img.shape[1]/4,img.shape[0]/4 #new size (w,h)
                    new_x = 512
                    new_y = new_x * img_ratio
                    img = cv2.resize(img,(new_x, int(new_y)))
                    print "Image resized :"
                    print new_x
                    print new_y

                if (img == None):                                      ## Check for invalid input
                        print "Could not open or find the image"
                else:
                        cascade = cv2.CascadeClassifier("/home/erogol/Desktop/rsom_face/haarcascade_frontalface_alt.xml")
                        gray = cv2.cvtColor(img, cv.CV_BGR2GRAY)
                        gray = cv2.equalizeHist(gray)
                        # cv2.namedWindow('Display image')          ## create window for display
                        # cv2.imshow('Display image', gray)          ## Show image in the window
                        # cv2.waitKey(0)                            ## Wait for keystroke
                        # cv2.destroyAllWindows()    
                        #pdb.set_trace()
        
                        rects = detect(gray, cascade)
                        
                        ## Extract face coordinates
                        if len(rects) == 0:
                            print "No face detected!!"
                        else:
                            for i,rect in enumerate(rects):
                                x1 = rect[1]
                                y1 = rect[0]
                                x2 = rect[3]
                                y2 = rect[2]
                                
                                ## Extract face ROI
                                faceROI = gray[x1:x2, y1:y2]

                                ## Show face ROI
                                cv2.namedWindow(str(i))         ## create window for display
                                cv2.imshow(str(i), faceROI)

                            vis = img.copy()
                            draw_rects(vis, rects, (0, 255, 0))

                            cv2.namedWindow('Display image')          ## create window for display
                            cv2.imshow('Display image', vis)          ## Show image in the window

                            print "size of image: ", img.shape        ## print size of image
                            cv2.waitKey(0)                            ## Wait for keystroke
                            cv2.destroyAllWindows()                   ## Destroy all windows