Moiré Backdoor Attack (MBA): A Novel Trigger for Pedestrian Detectors in the Physical World

A backdoor attack is executed by injecting a few poisoned samples into the training dataset of Deep Neural Networks (DNNs), enabling attackers to implant a hidden manipulation. This manipulation can be triggered during inference to exhibit controlled behavior, posing risks in real-world deployments. In this paper, we specifically focus on the safety-critical task of pedestrian detection and propose a novel backdoor trigger by exploiting the Moiré effect. The Moiré effect, a common physical phenomenon, disrupts camera-captured images by introducing Moiré patterns and unavoidable interference. Our method comprises three key steps. Firstly, we analyze the Moiré effect's cause and simulate its patterns on pedestrians' clothing. Next, we embed these Moiré patterns as a backdoor trigger into digital images and use this dataset to train a backdoored detector. Finally, we physically test the trained detector by wearing clothing that generates Moiré patterns. We demonstrate that individuals wearing such clothes can effectively evade detection by the backdoored model while wearing regular clothes does not trigger the attack, ensuring the attack remains covert. Extensive experiments in both digital and physical spaces thoroughly demonstrate the effectiveness and efficacy of our proposed Moiré Backdoor Attack.