"Eigenfaces for recognition," M Turk, A Pentland - Journal of Cognitive Neuroscience, 1991.

This paper propose a method call eigenface to recognize face in images. This method is fast, simple, and accuracy in constrained environment like household or office. The method decompose the face image into a small set of image call "eigenface" which is basically principle components of set of training face images. And then recognize is preform by project the query image into subspace spanned by enigenfaces.
The method is quite simple and fast, but it has a lot of constrain in image such as lightening and view of the face, which cause limit use in application. Despite of these constrain, it still has great learning ability and performance that let this paper become a classic one.