1. A face annotation method, adapted for an owner to annotate members in online social networks (OSNs), comprising: providing a Hierarchical Database Access (HDA) architecture for each member according to various social network contexts; providing a Fused Face Recognition (FFR) unit which uses an Adaboost algorithm to fuse a plurality types of base classifiers; and constructing a Face Recognizer by integrating the HDA architecture and the corresponding FFR unit for the owner and each member via respective types of the social network contexts; and selecting suitable personalized Face Recognizers and merging multiple personalized Face Recognizer results by using at least two collaborative FR strategies.