steganography: hiding data inside images

README

inspired by http://blog.wolfram.com/2010/07/08/doing-spy-stuff-with-mathematica/

requires CImg (http://cimg.sourceforge.net/reference/index.html)

lsbmessage.cc

#include <iostream>
#include <cstdio>
#include <string>

#include <CImg.h>

using namespace std;
using namespace cimg_library;

typedef CImg<unsigned char> ByteCImg;

void encode(const string& imgFilename, const FILE * input, const string& outputFilename);
void decode(const string& imgFilename, FILE * output);

int main(int argc, char ** argv) {

  string cmdname = string(argv[0]);
  
  if (argc > 3 || argc < 2) {
    cerr << "usage:" << endl
      << "ENCODE: " << cmdname << " CARRIER_IMAGE OUTPUT_FILENAME < MESSAGE_TO_HIDE" << endl
      << "DECODE: " << cmdname << " IMAGE_WITH_HIDDEN_MESSAGE > EXTRACTED_MESSAGE" << endl;
    return 1;
  }
  if (argc == 3) {
    string imgFilename(argv[1]);
    cerr << "Embedding in image: " << imgFilename << endl;
    string outputFilename(argv[2]);
    cerr << "Input from stdin, output to: " << outputFilename << endl;

    encode(imgFilename, stdin, outputFilename);
  } else {
    string imgFilename(argv[1]);
    cerr << "Decoding file: " << imgFilename << endl;

    decode(imgFilename, stdout);
  }
}

void encode(const string& imgFilename, const FILE * input, const string& outputFilename) {
  ByteCImg image(imgFilename.c_str());
  image &= 0xfe;

  ByteCImg::iterator it = image.begin();
  for (;;) {
    if (feof(stdin)) {
      break;
    }
    char cur = getc(stdin);

    for (int b = 0; b < 8; ++b) {
      if (it == image.end()) {
        break;
      }
      *it = *it | ((cur >> b) & 0x01);
      ++it;
    }
  }

  if (it == image.end()) {
    cerr << "Cannot fit the entire input in the image" << endl;
  }

  image.save(outputFilename.c_str());
}

void decode(const string& imgFilename, FILE * output) {

  ByteCImg image(imgFilename.c_str());

  char * buffer = (char*) malloc(sizeof(char) * image.size());
  int bufferpos = 0;
  
  int bit = 0;
  char chr = 0;
  for (ByteCImg::iterator it = image.begin(); it != image.end(); ++bit, ++it) {
    chr |= (*it & 0x01) << bit;
    if (bit == 7) {
      buffer[bufferpos++] = chr;
      // fputc((int) chr, output);
      bit = -1;
      chr = 0;
    }
  }

  for (; buffer[bufferpos] != EOF; --bufferpos);
  
  for (int i = 0; i < bufferpos; ++i) {
    fputc((int) buffer[i], output);
  }

}

Makefile

lsbmessage: lsbmessage.cc
	g++ -o lsbmessage lsbmessage.cc -O2 -L/usr/X11R6/lib -lm -lpthread -lX11