Code for Steganography: How to Hide Data in Images in Python Tutorial

steganography.py

import cv2
import numpy as np
import os

def to_bin(data):
    """Convert `data` to binary format as string"""
    if isinstance(data, str):
        return ''.join([ format(ord(i), "08b") for i in data ])
    elif isinstance(data, bytes) or isinstance(data, np.ndarray):
        return [ format(i, "08b") for i in data ]
    elif isinstance(data, int) or isinstance(data, np.uint8):
        return format(data, "08b")
    else:
        raise TypeError("Type not supported.")


def encode(image_name, secret_data):
    # read the image
    image = cv2.imread(image_name)
    # maximum bytes to encode
    n_bytes = image.shape[0] * image.shape[1] * 3 // 8
    print("[*] Maximum bytes to encode:", n_bytes)
    if len(secret_data) > n_bytes:
        raise ValueError("[!] Insufficient bytes, need bigger image or less data.")
    print("[*] Encoding data...")
    # add stopping criteria
    secret_data += "====="
    data_index = 0
    # convert data to binary
    binary_secret_data = to_bin(secret_data)
    # size of data to hide
    data_len = len(binary_secret_data)
    
    for row in image:
        for pixel in row:
            # convert RGB values to binary format
            r, g, b = to_bin(pixel)
            # modify the least significant bit only if there is still data to store
            if data_index < data_len:
                # least significant red pixel bit
                pixel[0] = int(r[:-1] + binary_secret_data[data_index], 2)
                data_index += 1
            if data_index < data_len:
                # least significant green pixel bit
                pixel[1] = int(g[:-1] + binary_secret_data[data_index], 2)
                data_index += 1
            if data_index < data_len:
                # least significant blue pixel bit
                pixel[2] = int(b[:-1] + binary_secret_data[data_index], 2)
                data_index += 1
            # if data is encoded, just break out of the loop
            if data_index >= data_len:
                break
    return image


def decode(image_name):
    print("[+] Decoding...")
    # read the image
    image = cv2.imread(image_name)
    binary_data = ""
    for row in image:
        for pixel in row:
            r, g, b = to_bin(pixel)
            binary_data += r[-1]
            binary_data += g[-1]
            binary_data += b[-1]

    # split by 8-bits
    all_bytes = [ binary_data[i: i+8] for i in range(0, len(binary_data), 8) ]
    # convert from bits to characters
    decoded_data = ""
    for byte in all_bytes:
        decoded_data += chr(int(byte, 2))
        if decoded_data[-5:] == "=====":
            break
    return decoded_data[:-5]


if __name__ == "__main__":
    import argparse
    parser = argparse.ArgumentParser(description="Steganography encoder/decoder, this Python scripts encode data within images.")
    parser.add_argument("-t", "--text", help="The text data to encode into the image, this only should be specified for encoding")
    parser.add_argument("-e", "--encode", help="Encode the following image")
    parser.add_argument("-d", "--decode", help="Decode the following image")
    
    args = parser.parse_args()
    secret_data = args.text
    if args.encode:
        # if the encode argument is specified
        input_image = args.encode
        print("input_image:", input_image)
        # split the absolute path and the file
        path, file = os.path.split(input_image)
        # split the filename and the image extension
        filename, ext = file.split(".")
        output_image = os.path.join(path, f"{filename}_encoded.{ext}")
        # encode the data into the image
        encoded_image = encode(image_name=input_image, secret_data=secret_data)
        # save the output image (encoded image)
        cv2.imwrite(output_image, encoded_image)
        print("[+] Saved encoded image.")
    if args.decode:
        input_image = args.decode
        # decode the secret data from the image
        decoded_data = decode(input_image)
        print("[+] Decoded data:", decoded_data)

steganography_advanced.py

import cv2
import numpy as np
import os

def to_bin(data):
    """Convert `data` to binary format as string"""
    if isinstance(data, str):
        return ''.join([ format(ord(i), "08b") for i in data ])
    elif isinstance(data, bytes):
        return ''.join([ format(i, "08b") for i in data ])
    elif isinstance(data, np.ndarray):
        return [ format(i, "08b") for i in data ]
    elif isinstance(data, int) or isinstance(data, np.uint8):
        return format(data, "08b")
    else:
        raise TypeError("Type not supported.")


def encode(image_name, secret_data, n_bits=2):
    # read the image
    image = cv2.imread(image_name)
    # maximum bytes to encode
    n_bytes = image.shape[0] * image.shape[1] * 3 * n_bits // 8
    print("[*] Maximum bytes to encode:", n_bytes)
    print("[*] Data size:", len(secret_data))
    if len(secret_data) > n_bytes:
        raise ValueError(f"[!] Insufficient bytes ({len(secret_data)}), need bigger image or less data.")
    print("[*] Encoding data...")
    # add stopping criteria
    if isinstance(secret_data, str):
        secret_data += "====="
    elif isinstance(secret_data, bytes):
        secret_data += b"====="
    data_index = 0
    # convert data to binary
    binary_secret_data = to_bin(secret_data)
    # size of data to hide
    data_len = len(binary_secret_data)
    for bit in range(1, n_bits+1):
        for row in image:
            for pixel in row:
                # convert RGB values to binary format
                r, g, b = to_bin(pixel)
                # modify the least significant bit only if there is still data to store
                if data_index < data_len:
                    if bit == 1:
                        # least significant red pixel bit    
                        pixel[0] = int(r[:-bit] + binary_secret_data[data_index], 2)
                    elif bit > 1:
                        # replace the `bit` least significant bit of the red pixel with the data bit
                        pixel[0] = int(r[:-bit] + binary_secret_data[data_index] + r[-bit+1:], 2)
                    data_index += 1
                if data_index < data_len:
                    if bit == 1:
                        # least significant green pixel bit
                        pixel[1] = int(g[:-bit] + binary_secret_data[data_index], 2)
                    elif bit > 1:
                        # replace the `bit` least significant bit of the green pixel with the data bit
                        pixel[1] = int(g[:-bit] + binary_secret_data[data_index] + g[-bit+1:], 2)
                    data_index += 1
                if data_index < data_len:
                    if bit == 1:
                        # least significant blue pixel bit
                        pixel[2] = int(b[:-bit] + binary_secret_data[data_index], 2)
                    elif bit > 1:
                        # replace the `bit` least significant bit of the blue pixel with the data bit
                        pixel[2] = int(b[:-bit] + binary_secret_data[data_index] + b[-bit+1:], 2)
                    data_index += 1
                # if data is encoded, just break out of the loop
                if data_index >= data_len:
                    break
    return image


def decode(image_name, n_bits=1, in_bytes=False):
    print("[+] Decoding...")
    # read the image
    image = cv2.imread(image_name)
    binary_data = ""
    for bit in range(1, n_bits+1):
        for row in image:
            for pixel in row:
                r, g, b = to_bin(pixel)
                binary_data += r[-bit]
                binary_data += g[-bit]
                binary_data += b[-bit]

    # split by 8-bits
    all_bytes = [ binary_data[i: i+8] for i in range(0, len(binary_data), 8) ]
    # convert from bits to characters
    if in_bytes:
        # if the data we'll decode is binary data, 
        # we initialize bytearray instead of string
        decoded_data = bytearray()
        for byte in all_bytes:
            # append the data after converting from binary
            decoded_data.append(int(byte, 2))
            if decoded_data[-5:] == b"=====":
                # exit out of the loop if we find the stopping criteria
                break
    else:
        decoded_data = ""
        for byte in all_bytes:
            decoded_data += chr(int(byte, 2))
            if decoded_data[-5:] == "=====":
                break
    return decoded_data[:-5]


if __name__ == "__main__":
    import argparse
    parser = argparse.ArgumentParser(description="Steganography encoder/decoder, this Python scripts encode data within images.")
    parser.add_argument("-t", "--text", help="The text data to encode into the image, this only should be specified for encoding")
    parser.add_argument("-f", "--file", help="The file to hide into the image, this only should be specified while encoding")
    parser.add_argument("-e", "--encode", help="Encode the following image")
    parser.add_argument("-d", "--decode", help="Decode the following image")
    parser.add_argument("-b", "--n-bits", help="The number of least significant bits of the image to encode", type=int, default=2)
    
    args = parser.parse_args()
    if args.encode:
        # if the encode argument is specified
        if args.text:
            secret_data = args.text
        elif args.file:
            with open(args.file, "rb") as f:
                secret_data = f.read()
        input_image = args.encode
        # split the absolute path and the file
        path, file = os.path.split(input_image)
        # split the filename and the image extension
        filename, ext = file.split(".")
        output_image = os.path.join(path, f"{filename}_encoded.{ext}")
        # encode the data into the image
        encoded_image = encode(image_name=input_image, secret_data=secret_data, n_bits=args.n_bits)
        # save the output image (encoded image)
        cv2.imwrite(output_image, encoded_image)
        print("[+] Saved encoded image.")
    if args.decode:
        input_image = args.decode
        if args.file:
            # decode the secret data from the image and write it to file
            decoded_data = decode(input_image, n_bits=args.n_bits, in_bytes=True)
            with open(args.file, "wb") as f:
                f.write(decoded_data)
            print(f"[+] File decoded, {args.file} is saved successfully.")
        else:
            # decode the secret data from the image and print it in the console
            decoded_data = decode(input_image, n_bits=args.n_bits)
            print("[+] Decoded data:", decoded_data)

To run this, you should install:

pip3 install opencv-python numpy

Try running script help:

python steganography.py --help

Output:

usage: steganography.py [-h] [-t TEXT] [-e ENCODE] [-d DECODE]

Steganography encoder/decoder, this Python scripts encode data within images.

optional arguments:
-h, --help            show this help message and exit
-t TEXT, --text TEXT  The text data to encode into the image, this only
                        should be specified for encoding
-e ENCODE, --encode ENCODE
                        Encode the following image
-d DECODE, --decode DECODE
                        Decode the following image

To encode some data to the image named image.PNG:

python steganography.py -e image.PNG -t "This is some secret data."

This will write another image named imaged_encoded.PNG with data encoded in it and outputs:

[*] Maximum bytes to encode: 125028
[*] Encoding data...
[+] Saved encoded image.

To decode the data containing the image named encoded_image.PNG, use:

python steganography.py -d encoded_image.PNG

Outputs:

[+] Decoding...
[+] Decoded data: This is some secret data.