Disclaimer!

This project is 100%, absolutely vibe-coded using Opus 5.5.

melu

A content-bound image watermarking system.

pip install -e .            # or: pip install -e ".[gpu]" for the torch backend (CUDA)
melu embed  photo.png marked.png --salt "my secret"
melu detect marked.png --salt "my secret"        # exit 0 = found, 1 = not found
melu torture marked.png --salt "my secret" --crops

import melu
marked, info = melu.embed("photo.png", salt="my secret")
marked.save("marked.png")                 # colour untouched, only luma carries the mark
r = melu.detect("marked.png", salt="my secret")
print(r.found, r.score, r.route)           # True 3.3 'A'

Things to know

• Keep the salt secret. Anyone holding it can detect, and can attack the salt-only signals more easily.
• Check info.robust after embedding: tiny or flat images may not reach the threshold at the PSNR floor (the CLI refuses to write those unless --force).
• GPU. With torch and CUDA installed the searches run on the GPU automatically (about 2 s per marked image, 2–10 s for an unmarked one on an RTX 4060). CBWM_GPU=0 forces numpy, CBWM_WORKERS sets FFT threads.

Tests

pip install -e ".[test]" then pytest. The package must reproduce the lab code exactly on a synthetic image (tests/golden.json), find marks after a quarter crop and a 3° rotation, and stay silent on unmarked images and wrong salts.