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nelsonblaha/

neocaptcha-motion-attack

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A Python proof-of-concept decodes a motion-noise CAPTCHA using a fixed pipeline (no ML). It demonstrates a reproducible filter approach rather than per-challenge learning.

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2026since
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Reviewgenerated from repository data · Jul 18, 2026

What it is

A fixed, ~150-line Python script (no machine learning, no training data) that turns a motion noise CAPTCHA into an answer by applying a sequence of image processing steps and OCR. The repo provides a concrete pipeline and a sample video to reproduce results.

How it works

The pipeline (solve.py) performs:

  1. Decode frames from the input video.
  2. Auto-detect the animated region with high temporal variance.
  3. Apply a spatial high-pass filter to each frame.
  4. Do dense block-matching between consecutive frames to estimate local motion (magnitude of shift).
  5. Short-window average and median de-band to produce filled glyphs.
  6. Run tesseract OCR with majority voting to produce the final answer. All steps 3–5 are described as identical across challenges, implying a fixed filter rather than per-challenge learning.

Getting started

Reproduce instructions from the README:

# needs: python3 (numpy, pillow), ffmpeg, tesseract
pip install numpy pillow
python3 solve.py captcha.mp4 out
# -> prints SOLUTION: AT ; writes out/solved_montage.png and out/solved.gif

Recent releases

  • none

Traction

Stars: 16

Behind the repo

No linked startup or company information provided in the repository data.

Caveats

  • License: none listed
  • Language: Python
  • Created: 2026-07-15
  • Last push: 2026-07-15
  • Reproduces on a lossy sample video; the note clarifies this is a lower bound on exposure of the real CAPTCHA against uncompressed streams.
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