StringSet Info::standardKeys()
{
    static StringSet res;

    if ( !res.empty() )
        return res;

    QList<const Exiv2::TagInfo*> tags;
    tags <<
        Exiv2::ExifTags::ifdTagList() <<
        Exiv2::ExifTags::exifTagList() <<
        Exiv2::ExifTags::iopTagList() <<
        Exiv2::ExifTags::gpsTagList();
    for (QList<const Exiv2::TagInfo*>::iterator it = tags.begin(); it != tags.end(); ++it ) {
        while ( (*it)->tag_ != 0xffff ) {
            res.insert( Exiv2::ExifKey( (*it)->tag_, Exiv2::ExifTags::ifdItem( (*it)->ifdId_ ) ).key().c_str() );
            ++(*it);
        }
    }

    // Now the ugly part -- exiv2 doesn't have any way to get a list of
    // MakerNote tags in a reasonable form, so we have to parse it from strings
    
    std::ostringstream s;
    for ( Exiv2::IfdId kind = Exiv2::canonIfdId; kind < Exiv2::lastIfdId;
            kind = static_cast<Exiv2::IfdId>( kind + 1 ) ) {
        Exiv2::ExifTags::makerTaglist( s, kind );
    }

    QStringList lines = QString( s.str().c_str() ).split( '\n' );
    for ( QStringList::const_iterator it = lines.begin(); it != lines.end(); ++it ) {
        if ( it->isEmpty() )
            continue;
        QStringList fields = it->split( '\t' );
        if ( fields.size() != 7 ) {
            kDebug() << "Unparsable output from exiv2 library: " << *it;
            continue;
        }
        QString id = fields[4];
        if ( id.endsWith( ',' ) )
            id.chop(1);
        res.insert( id );
    }

    return res;
}