Lazy solution... like pseudoprototype.

gistfile1.js

var WebCam = { 
  capturing: false,
  callbacks: [], 

  capture: function(cb) {
    addCallback(cb);
    _takePic();
  },  

  addCallback(cb) {
    this.callbacks.push(cb);
  },  

  _takePic: function() {
    if (this.capturing) {
      return;
    }   

    //ugly but I don't want to think
    that=this;
    this.capturing = true;
    filename = new Date().getTime() + ".jpg";
    cameraConfig.output = cameraFilePath + name;
    var camera = new RaspiCam(cameraConfig);
    camera.on("change", debounce(camera.stop, debounceTime));
    camera.on("exit", function(){
      while (cb = that.callbacks.shift()) {
        cb(err, filename);
      }   
      that.capturing = false;
    }); 
    camera.start();
  },  
};

exports.photo = function(request, response){
  WebCam.capture(function(err, filename) {
    if (err) {
      response.send({message: err, name: filename});
    } else {
      response.send({message: "Successfully captured image", name: name});
    }   
  }); 
}