What are the high level steps to classify a facial expression?

edit

I want to tell if a face in an image is smiling or winking or shouting etc...

I have made an program that works quite well that does the following:

1. Find the face rectangle using the usual methods (e.g. haarcascade_frontalface_alt.xml)
2. Crop the face and account for rotations
3. Resize to a fixed size.
4. Filter the image (e.g. blur & equalise the histograms etc..)
5. Run a series of custom HAAR classifiers once on the resultant image (e.g. smile classifier, wink classifier... etc)
6. Choose the expression with the highest score.

Are there other method I can be using? I have seen SVM and Gabor vector mentioned elsewhere but I don't know how they work.