Face Detective is a free software that can extract faces from photos, and store them as separate images. You just need to specify the folder in which all your photos are located. Face Detective will then scan the folder to find which of the photos have faces, and will then extract those faces separately.
It is extremely easy to use Face Detective. When you run the software, you need to press “Play” button on its toolbar. At that time, Face Detective will prompt you to provide folder path where your photos are located. Face Detective will then scan all those photos. If it finds any face, it will extract and crop that, and will store as a thumbnail in My Documents folder.
Download Face Detective here.