Hello
I can create the face detection software for you, face detection plugin is available for jquery and works on both videos and images so that can be used for detection in browser.
Also face detection works in php (with and without opencv) so I can create a facedetection php script that takes in either image or video clip and returns the number of faces.
The php script can be created into a proper api.
Also I can do the same with node.js (if you think that is better)
Lets discuss this further on chat.
Thanks
Dinesh Chand