  Face anti-spoofing is designed to keep face recognition systems from
recognizing fake faces as the genuine users. While advanced face anti-spoofing
methods are developed, new types of spoof attacks are also being created and
becoming a threat to all existing systems. We define the detection of unknown
spoof attacks as Zero-Shot Face Anti-spoofing (ZSFA). Previous works of ZSFA
only study 1-2 types of spoof attacks, such as print/replay attacks, which
limits the insight of this problem. In this work, we expand the ZSFA problem to
a wide range of 13 types of spoof attacks, including print attack, replay
attack, 3D mask attacks, and so on. A novel Deep Tree Network (DTN) is proposed
to tackle the ZSFA. The tree is learned to partition the spoof samples into
semantic sub-groups in an unsupervised fashion. When a data sample arrives,
being know or unknown attacks, DTN routes it to the most similar spoof cluster,
and make the binary decision. In addition, to enable the study of ZSFA, we
introduce the first face anti-spoofing database that contains diverse types of
spoof attacks. Experiments show that our proposed method achieves the state of
the art on multiple testing protocols of ZSFA.
