README

A PHP 8.5+ library for invisible anti-counterfeiting of images using LSB (Least Significant Bit) Steganography. This library hides a secret message inside an image file, invisible to the human eye.

Features

• ✅ Invisible: Modifies only the Least Significant Bits (LSB) of RGB pixel values
• ✅ Compression: Compresses messages using Zlib before embedding
• ✅ Unicode Support: Full support for UTF-8, including CJK characters and emoji
• ✅ Dual Driver Support: Prioritizes Imagick, falls back to GD automatically
• ✅ Format Support: Reads JPG, PNG, GIF, WebP, BMP as source images
• ✅ Lossless Output: Always outputs as PNG to preserve hidden data
• ✅ PHP 8.5+: Uses modern PHP features (typed constants, readonly properties, match expressions)
• ✅ Composer Ready: PSR-4 autoloading, ready for integration

Requirements

• PHP >= 8.5
• ext-zlib (for compression)
• ext-imagick (recommended) OR ext-gd (at least one is required)

Installation

composer require pateon/steganography

Usage

Basic Usage

use Steganography\Processor;

$processor = new Processor();

// Encode a message into an image
$image = $processor->encode('source.jpg', 'This is my secret message! 秘密訊息');
$image->save('output.png'); // MUST save as PNG (lossless)

// Decode the message from the image
$message = $processor->decode('output.png');
echo $message; // "This is my secret message! 秘密訊息"

Force Specific Adapter

$processor = new Processor();

// Force GD
$processor->setPreferredAdapter('gd');

// Force Imagick
$processor->setPreferredAdapter('imagick');

Calculate Maximum Message Size

$processor = new Processor();
$maxBytes = $processor->calculateMaxMessageSize('source.jpg');
echo "Max message size: ~{$maxBytes} bytes";

Custom Compressor

use Steganography\Processor;
use Steganography\Compressor\ZlibCompressor;

$processor = new Processor(
    compressor: new ZlibCompressor(level: 9) // Maximum compression
);

⚠️ Important Notes

1. Output Format: Always save encoded images as PNG. JPG compression is lossy and will destroy the hidden data.

2. Source Format: JPG, PNG, GIF, WebP, and BMP are supported as source images.

3. Image Size: Larger images can store more data. Use calculateMaxMessageSize() to check capacity.

4. Imagick vs GD: Imagick is preferred for better performance. GD is used as fallback.

Architecture

src/
├── Processor.php              # Main entry point
├── Compressor/
│   ├── CompressorInterface.php
│   └── ZlibCompressor.php     # Zlib compression
├── Encoder/
│   ├── EncoderInterface.php
│   └── DefaultEncoder.php     # Base64 + Binary encoding
├── Exception/
│   ├── SteganographyException.php
│   ├── ImageTooSmallException.php
│   └── DecodeException.php
├── Image/
│   ├── Image.php              # LSB steganography logic
│   ├── Color.php              # RGBA color DTO
│   └── Adapter/
│       ├── ImageAdapterInterface.php
│       ├── GdAdapter.php      # GD implementation
│       └── ImagickAdapter.php # Imagick implementation
└── Iterator/
    ├── BinaryIterator.php     # Binary data iterator
    └── RectIterator.php       # Pixel coordinate iterator

How It Works

1. Compression: The message is compressed using Zlib
2. Encoding: Compressed data is Base64 encoded, then converted to binary (0s and 1s)
3. Embedding: Each pixel's RGB values have their LSB modified to store 3 bits (1 per channel)
4. Header: A 48-bit length header is prepended to know how much data to read when decoding

License

MIT License - see LICENSE file