Stegstr

Stegstr hides Nostr messages and arbitrary payloads inside PNG images using steganography. Users embed their feed (posts, DMs, JSON) into images and share them; recipients use Detect to load the hidden content. No registration, works offline.

When to use this skill

User wants to decode (extract) hidden data from a PNG that contains Stegstr data.
User wants to embed a payload into a cover PNG (e.g. Nostr bundle, JSON, text).
User mentions steganography, Nostr-in-images, Stegstr, hiding data in images, or secret messages in photos.
User needs programmatic access for automation, scripts, or AI agents.

CLI (headless)

Build the CLI from the Stegstr repo:

git clone https://github.com/brunkstr/Stegstr.git
cd Stegstr/src-tauri
cargo build --release --bin stegstr-cli

Binary: target/release/stegstr-cli (or stegstr-cli.exe on Windows).

Decode (extract payload)

stegstr-cli decode image.png

Writes raw payload to stdout. Valid UTF-8 JSON is printed as text; otherwise base64:<data>. Exit 0 on success.

Detect (decode + decrypt app bundle)

stegstr-cli detect image.png

Decodes and decrypts; prints Nostr bundle JSON { "version": 1, "events": [...] }.

Embed (hide payload in image)

stegstr-cli embed cover.png -o out.png --payload "text or JSON"
stegstr-cli embed cover.png -o out.png --payload @bundle.json
stegstr-cli embed cover.png -o out.png --payload @bundle.json --encrypt

Use --payload @file to load from file. Use --encrypt so any Stegstr user can detect. Use --payload-base64 <base64> for binary payloads.

Post (create kind 1 note bundle)

stegstr-cli post "Your message here" --output bundle.json
stegstr-cli post "Message" --privkey-hex <64-char-hex> --output bundle.json

Creates a Nostr bundle; use stegstr-cli embed to hide it in an image.

Example workflow

# Create a post bundle
stegstr-cli post "Hello from OpenClaw" --output bundle.json

# Embed into a cover image (encrypted for any Stegstr user)
stegstr-cli embed cover.png -o stego.png --payload @bundle.json --encrypt

# Recipient detects and extracts
stegstr-cli detect stego.png

Image format

PNG only (lossless). JPEG or other lossy formats will corrupt the hidden data.

Payload format

Magic: STEGSTR (7 bytes ASCII)
Length: 4 bytes, big-endian
Payload: UTF-8 JSON or raw bytes (desktop app encrypts; CLI can embed raw or --encrypt)

Decrypted bundle: { "version": 1, "events": [ ... Nostr events ... ] }. Schema: bundle.schema.json.