Real-time face recognition is a relatively non-trivial process and as a result most people use a range of popular libraries, such as OpenCV. However, there seem to be few options for targetting Windows 10 platforms for Universal Applications.
Support now seems to be available for OpenCV and Universal Apps but I have had quite a bit of difficulty getting this setup and I really only require the face recognition features.
What libraries currently provide support for developing real-time face recognition applications for Windows 10 and Universal Applications?
I would go down the OpenCV route, it's the most popular one so there is a lot of support for it if your problem isn't platform specific.
If there's no requirement for offline use, checkout Project Oxford, it's really cool.
Alternatively, if javascript is an option, there are a whole lot of libraries out there. I've used headtrackr, which worked well with Windows 8/WinJS 1.0.