by Tomas Alvarez (http://twitter.com/alvarez_tomas)
Face.js is a OpenCV Haar algorithm implementation for Javascript, in-progress right now, which aims to provide a simple way 
to detect faces in a picture.

git clone git://github.com/talvarez/Face.js.git
node-waf configure build

var Face = require('../build/default/face.node'),
detector = new Face.init();

detector.img = '/tmp/last.png';
console.log(detector.img);

detector.oncomplete = function(faces){

	console.log("I found " + faces.length + " faces");
	for(var i = 0; i < faces.length; i++) {
			console.log(faces[i].x, faces[i].y, faces[i].width, faces[i].height);
	}

};

detector.run();

var Face = require('../build/default/face.node'),
recognizer = new Face.init(),
Canvas = require('../deps/canvas/canvas.js'),
Image = Canvas.Image,
canvas = new Canvas(800, 600),
ctx = canvas.getContext('2d');


function boundFaces(input, faces, res) {
	var img = new Image;

	img.onload = function(){
			ctx.drawImage(img, 0, 0);
	}


	var threshold_false_smile = 15;
	img.src = input;

	for(var i = 0; i < faces.length; i++) {

			res.write('Intensity: '+faces[i].intensity+'<BR>');

			if(faces[i].smile) {
					if(faces[i].intensity > threshold_false_smile) { //Threshold possible false positives smiles
							ctx.strokeStyle = 'rgb(0, 255, 0)';
					} else {
							ctx.strokeStyle = 'rgb(255, 0, 0)';
					}
			} else {

					ctx.strokeStyle = 'rgb(255, 0, 0)';
			}

			ctx.strokeRect(faces[i].x, faces[i].y, faces[i].width, faces[i].height);
	}
}


function getFaces(res) {

	recognizer.img = './samples/frame5.png';
	recognizer.pathto = '../cascades/';

	recognizer.checkSmile = true;
	recognizer.minsize = 20;

	recognizer.oncomplete = function(faces){

			boundFaces(recognizer.img, faces, res);
			res.write("I found " + faces.length + " faces <BR>");
			res.end('<img src="' + canvas.toDataURL() + '" />');

	};

	recognizer.run();

}

var http = require('http');
http.createServer(function (req, res) {
			res.writeHead(200, { 'Content-Type': 'text/html' });
			res.write("Getting faces...<BR>");
			getFaces(res);

}).listen(3000);

console.log('Server started on port 3000');


Setting 'checkSmile' true, it will scan the previously detected face and search a possible smile gesture.
The faces object now includes a property, called 'smile' in case it's true another new property will be added to the object, called 'intensity'.
'intensity' property is used for control possible false positives smiles, maybe the detector detect a smile, but its wrong (this is common in computer
vision programs, because the detectors handles a lot of variables like, illumination, pose, size) so you can threshold it.
You can set a minimum, and a maximum too, size for a face, if you dont provide it, Face.js will set it to 20 for the min, and 0 for the max (0 means all the sizes in the maxsize property).

NOTE: It uses node-canvas, but is not necessary, I used it (and I include it in deps) just for draw rectangles in the faces areas.

- node 0.4.8
- opencv 2.2.0