opencv的人脸检测功能在一般场合还是不错的。而ubuntu正好提供了python-opencv这个包，用它可以方便地实现人脸检测的代码。
写代码之前应该先安装python-opencv：
代码如下:
$ sudo apt-get install python-opencv
具体原理就不多说了，可以参考一下这篇文章。直接上源码。
代码如下:
#!/usr/bin/python# -*- coding: utf-8 -*-
# face_detect.py
# face detection using opencv. based on sample code from:# http://python.pastebin.com/m76db1d6b
# usage: python face_detect.py
import sys, osfrom opencv.cv import *from opencv.highgui import *from pil import image, imagedrawfrom math import sqrt
def detectobjects(image): “””converts an image to grayscale and prints the locations of any faces found””” grayscale = cvcreateimage(cvsize(image.width, image.height), 8, 1) cvcvtcolor(image, grayscale, cv_bgr2gray)
storage = cvcreatememstorage(0) cvclearmemstorage(storage) cvequalizehist(grayscale, grayscale)
cascade = cvloadhaarclassifiercascade( ‘/usr/share/opencv/haarcascades/haarcascade_frontalface_default.xml’, cvsize(1,1)) faces = cvhaardetectobjects(grayscale, cascade, storage, 1.1, 2, cv_haar_do_canny_pruning, cvsize(20,20))
result = [] for f in faces: result.append((f.x, f.y, f.x+f.width, f.y+f.height))
return result
def grayscale(r, g, b): return int(r * .3 + g * .59 + b * .11)
def process(infile, outfile):
image = cvloadimage(infile); if image: faces = detectobjects(image)
im = image.open(infile)
if faces: draw = imagedraw.draw(im) for f in faces: draw.rectangle(f, outline=(255, 0, 255))
im.save(outfile, “jpeg”, quality=100) else: print “error: cannot detect faces on %s” % infile
if __name__ == “__main__”: process(‘input.jpg’, ‘output.jpg’)