Well, it isn't the best approach using those algorithms as face recognition. To some extent those algorithms could be used for face recognition, however I would predict them to be super slow and might sometimes give false positive matches or no matches at all, it would be better to use something like eigen faces or fisher faces, algorithms which are designed to do just that.
That's only for recognizing, but before face recognition you have to find the face in the image, for that you have to use something like cascade classifiers, in opencv you have already some Haar classifiers inside for detecting faces. Basically first step for you would be to detect faces.
Here are couple links to get you started with recognition:
When I made my face recognition application, the biggest help to understand and program it came from the first link, even though it's in old openCV.