Domain-adaptive Energy-based Models for Generalizable Face Anti-Spoofing

Face anti-spoofing (FAS) plays a crucial role in securing face recognition systems against presentation attacks. However, existing FAS methods often struggle to generalize to unseen attacks and domains. Existing generalizable FAS studies generally leverage domain generalization (DG) techniques for exploiting intermediate features that support generalization while neglecting the task-specific nature of FAS. In this paper, we argue that the FAS task is an imbalanced classification problem, which renders it unsuitable to be handled by a standard discriminative classifier. In contrast, we propose a novel approach for FAS by modeling the problem from a generative perspective using an energy-based model (EBM). The EBM captures the distribution of genuine faces and detects spoofing attempts as deviations from this distribution. We train the EBM using a discriminative objective and an energy regularization term to shape the learned distribution and improve generalization. To enhance the robustness to unseen domains, we introduce an energy-based domain augmentation technique that explores the latent space around the source distribution guided by the EBM. We further leverage a meta-learning framework and a gradient-based variant to leverage the augmented data for domain generalization. For practicability, we consider a practical setting where samples are holistically collected under different environments without distinct domain labels, and show that our method can naturally harness this challenging setting by training with cluster labels. Extensive experiments on four FAS datasets demonstrate the superiority of our method in both intra- and cross-dataset settings, outperforming state-of-the-art approaches.