There have been recent reports of Google capturing image data prior to launching Street View in Europe. In conjunction to this, concerns were raised regarding the different (and stricter) privacy laws in Europe. A blog post about Google starting experiments to blur faces in its Street View images falls neatly into place given these speculations. This will be a really challenging face detection task. Taking into account that missing faces might still lead to privacy issues (and wrongly identifying non-faces as faces having an equally bad affect), I would not be surprised if some sort of manual input is built into the system. A couple of images from the blog (note the blurred out faces):