A second, complementary, approach relies on post-hoc machine learning and forensic anal-ysis to passively identify statistical and physical artifacts left behind by media manipulation.For example, learning-based forensic analysis techniques use machine learning to automati-cally detect manipulated visual and auditory content (see e.g. [94]). However, these learning-based approaches have been shown to be vulnerable to adversarial attacks [95] and contextshift [96]. Artifact-based techniques exploit low-level pixel artifacts introduced during synthe-sis. But these techniques are vulnerable to counter-measures like recompression or additivenoise. Other approaches involve biometric features of an individual (e.g., the unique motionproduced by the ears in synchrony with speech [97]) or behavioral mannerisms [98]). Biomet-ric and behavioral approaches are robust to compression changes and do not rely on assump-tions about the moment of media capture, but they do not scale well. However, they may bevulnerable to future generative-AI systems that may adapt and synthesize individual biometricsignals.