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Perceptual Hashing

Intentionally maximizes the change of hash collision to detect similar images. Used by Google's Search by Image feature or Apple's CSAM. Perceptual Hashing

Algorithms and Their Performances​

Zauner​

  • Fastest: block-mean-based perceptual image hash.
  • Most discriminative: Marr-Hildreth operator-based hash function

Vulnerabilities​

It's Not What It Looks Like: Manipulating Perceptual Hashing-based Applications​

  • TLDR: A delicately designed image can fool a perceptual hash application, making it classify two completely different images as the same.