I think these QR codes are just otpauth:// URLs.

In a demo of implementing TOTP yourself, I implemented this and now I see that I even released this onto CPAN as Auth::GoogleAuthenticator. The meat of the code is:

sub registration_qr_code {
    my ($self, $label, $type) = @_;
    # if we have an OTP, dislay the QRCode to the user
    require Imager::QRCode;
    my $qrcode = Imager::QRCode->new(
        size => 4,
        margin => 4,
        version => 1,
        level => 'M',
        casesensitive => 1,
    );
    my $img = $qrcode->plot($self->registration_url($label, $type));
    $img->write( data => \my $res, type => 'png' );
    $res
}

sub registration_key {
    return encode_base32( $_[0]->{secret} );
}

sub registration_url {
    my ($self, $label, $type) = @_;
    $type ||= 'totp';
    $label= uri_escape($label);
    return "otpauth://$type/$label?secret=" . $self->registration_key
}
[download]

You can find the code also on Github