ai_meta

ai_meta is a small C11 library (and CLI) for detecting, extracting, stripping, and writing AI-generation metadata declared in image files.

• Repository: https://github.com/localtools/ai-meta
• License: MIT — free and open source
• Scope: declared metadata only — it does not analyze pixels to guess whether an undeclared image is AI-generated

Why

Generators and platforms increasingly embed provenance and generation parameters (Stable Diffusion parameters, EXIF/XMP, C2PA Content Credentials, IPTC). This library gives applications a dependency-light way to inspect and scrub that metadata while leaving pixel data and color profiles intact when requested.

Features

Scheme	Status	Notes
PNG tEXt / iTXt / zTXt	Supported	SD/A1111-style parameters; zlib inflate for compressed text; field expansion (prompt, Steps, Seed, …)
EXIF (basic)	Supported	Software, UserComment, ImageDescription, Artist, Make/Model — JPEG APP1, PNG eXIf, WebP EXIF
XMP (basic)	Supported	Property hints (CreatorTool, DigitalSourceType, …) + AI heuristics
C2PA	Detect / strip / hints	PNG caBX JUMBF + JPEG APP11; generator / trainedAlgorithmicMedia hints; no signature verification yet
IPTC	Supported (JPEG)	Photoshop APP13 IRB 0x0404 — Keywords, Caption, Headline, Byline

Formats: PNG, JPEG, WebP.

Quick start

Requirements

• C11 compiler (cc, clang, or gcc)
• zlib development headers (zlib1g-dev on Debian/Ubuntu; usually present on macOS)
• make (optional: CMake 3.16+)

Build & test

git clone https://github.com/localtools/ai-meta.git
cd ai-meta
make          # static lib, CLI, fixtures, tests
make test

Artifacts land in build/:

Path	Description
build/libai_meta.a	Static library
build/libai_meta.dylib / .so	Shared library (make shared)
build/ai_meta	Command-line tool

Release package (local)

make dist    # or: make package

Creates dist/ai_meta-<version>-<os>-<arch>.tar.gz with headers, static/shared libraries, CLI, relocatable pkg-config file, and license docs.

GitHub Releases are built automatically when you push a version tag (v*). Assets include Linux x86_64 and macOS arm64 tarballs plus SHA256SUMS.

git tag v0.1.0
git push origin v0.1.0
# → Actions workflow "release" builds, tests, and attaches artifacts

Install (system-wide)

sudo make install          # PREFIX=/usr/local by default
pkg-config --cflags --libs ai_meta

sudo make uninstall

CLI

./build/ai_meta scan path/to/image.png
./build/ai_meta extract path/to/image.png
./build/ai_meta strip path/to/in.png path/to/out.png [--keep-non-ai]
./build/ai_meta write path/to/in.png path/to/out.png parameters "Steps: 10, Seed: 1"

Link against the library

cc -Iinclude -o app app.c build/libai_meta.a -lz
# or after install:
cc $(pkg-config --cflags ai_meta) -o app app.c $(pkg-config --libs ai_meta)

See examples/basic.c.

C API

Public header: include/ai_meta.h.

Primary API is buffer-based (caller owns input). Optional *_file helpers perform I/O.

#include "ai_meta.h"

ai_meta_scan_result scan;
if (ai_meta_scan(buf, len, &scan) == AI_META_OK) {
    /* scan.format, scan.schemes (bitmask), scan.likely_ai */
}

ai_meta_info *info = NULL;
if (ai_meta_extract(buf, len, &info) == AI_META_OK) {
    for (size_t i = 0; i < info->field_count; i++)
        printf("%s = %s\n", info->fields[i].key, info->fields[i].value);
    ai_meta_info_free(info);
}

uint8_t *out = NULL;
size_t out_len = 0;
unsigned flags = AI_META_FLAG_STRIP_ALL_AI | AI_META_FLAG_KEEP_COLOR_PROFILE;
if (ai_meta_strip(buf, len, flags, &out, &out_len) == AI_META_OK) {
    /* write out[0..out_len) */
    ai_meta_buffer_free(out);
}

if (ai_meta_write(buf, len, "parameters", "Steps: 20, Seed: 1", &out, &out_len) == AI_META_OK)
    ai_meta_buffer_free(out);

Conventions

Topic	Rule
Errors	ai_meta_err (0 = OK); ai_meta_strerror()
Memory	ai_meta_info_free() / ai_meta_buffer_free() for library-allocated results
Strip / write	Always return a new buffer — input is never mutated in place
Color profiles	Preserved when AI_META_FLAG_KEEP_COLOR_PROFILE is set (recommended)

Design

• I/O: optional — core ops take buffers; *_file helpers wrap stdio
• Dependencies: zlib only (compressed PNG text); no libpng / libjpeg / libexif required
• Portability: Linux, macOS; Windows via a C11 toolchain (MSVC/MinGW) with zlib
• Safety: malformed / truncated metadata should fail gracefully (no crash); see truncation smoke tests

Out of scope

• Pixel / ML-based “is this AI?” detection
• Full C2PA claim verification and signing
• Lossy re-encode of image payloads (metadata containers only)
• Guaranteed round-trip of every exotic EXIF MakerNote

Testing

make test

Fixtures are generated under tests/fixtures/ (gitignored). Coverage includes clean images, SD parameters, benign text keep, XMP, IPTC, zTXt inflate, truncation smoke, and round-trip write.

CI runs on Ubuntu and macOS: .github/workflows/ci.yml.

Project layout

include/ai_meta.h     Public API
src/                  Library implementation
tools/ai_meta_cli.c   CLI
examples/basic.c      Minimal consumer
tests/                Unit tests + fixture generator
ai_meta.pc.in         pkg-config template

Contributing

Contributions are welcome. See CONTRIBUTING.md and our Code of Conduct.

For security issues, see SECURITY.md — please do not open public issues for vulnerabilities.

Changelog

See CHANGELOG.md.

License

This project is licensed under the MIT License — see LICENSE.

Copyright (c) 2026 Local Tools and ai_meta contributors

You may use, modify, and distribute this software under the terms of that license.