FaceLinkGen: A Re-evaluation of Identity Leakage in Privacy-Preserving Face Recognition and Face Anonymization Systems Using Simple Distillation

Privacy-preserving face recognition (PPFR) and face anonymization have different goals, but both must retain some identity-related information for their intended use. We show that an adaptive attacker can learn this information. We propose FaceLinkGen, a simple distillation-based attack that trains a face recognition model to map protected inputs back to standard face embeddings. FaceLinkGen applies to keyless PPFR systems and perception-preserving face de-identification (De-ID) systems. For PPFR, the recovered embeddings can be used to regenerate faces that match the original person. Across MinusFace, PartialFace, and DecoyFace, the regenerated faces achieve acceptance rates of 81.0--99.4\% on Face++ and 74.9--99.6\% on Amazon. For De-ID, FaceLinkGen links protected faces to unprotected images of the same person, reaching Recall@1 values of 48.4--89.6\% in the one-side-protected setting across the evaluated methods. FaceLinkGen exposes identity leakage across all evaluated methods, including DecoyFace and WDP, whose protection resists the tested U-Net attacks on face recovery and protected-to-unprotected linkage, respectively. The attack also remains effective when trained with limited paired data. Code is available at https://github.com/weathon/FaceLinkGenRelease.