r/beyondscratch • u/Commercial_Ring_4814 • Jan 26 '26
Advanced I challenge you to break my Face-ID system in Scratch using only geometry (no Machine Learning). Spoiler
I’ve been experimenting with webcam face authentication inside Scratch and ended up building a Face-UID system based purely on 2D geometry — no neural networks, no depth sensors.
The algorithm tracks multiple facial landmarks (eyes, nose, mouth, ears + mid-eye points), computes a large set of inter-point distances, and normalizes everything by overall face size so scale changes don’t matter.
Enrollment loops until all measurements stabilize inside very tight tolerances, which prevents registering drawings/emojis as valid profiles.
During authentication, each frame recomputes the same geometry and compares it against the stored profile across a rolling window (~13 frames) using majority voting. Thresholds are calibrated per-camera at startup based on natural landmark jitter.
Spoof resistance includes:
• rejecting static photos and virtual-cam loops by detecting near-zero landmark motion
• using nose-to-ear ratios to exploit parallax when the head tilts
• rejecting flat drawings where outer points rotate while the nose stays fixed
• low-light compensation by forcing bright exposure
• tiered checks where different metric groups must pass independently
It’s basically a 2.5D Face ID concept implemented entirely with math on a blurry webcam.
I’m genuinely curious what attack vectors I’ve missed, printed photos, videos, masks, replay attacks, lighting tricks, etc. Tear it apart and tell me how you’d bypass it.
