Exiv2

// ***************************************************************** -*- C++ -*-

// *****************************************************************************

// included header files

#include "exif.hpp"

#include <iostream>

#include <iomanip>

using namespace Exiv2;

// *****************************************************************************

// Main

int main(int argc, char* const argv[])

try {

    if( argc != 2 ){

        std::cerr << "Usage: test file.jpg" << std::endl;

        return 1;

    }

    Exiv2::ExifData exifData;

    exifData.read(argv[1]);

    ExifKey exifKey("Exif.Image.ImageDescription");

    Value::AutoPtr value = Value::create(asciiString);

    value->read("I don't really know");

    ExifData::iterator iter = exifData.findKey(exifKey);

    if (iter != exifData.end()) {

        iter->setValue(value.get());

    }

    else {

        exifData.add(exifKey, value.get());

    }

    exifData.write(argv[1]);

    return 0;

}

catch (Exiv2::Error& e) {

    std::cout << "Caught Exiv2 exception '" << e << "'\n";

    return -1;

}