\documentclass[12pt,a4paper]{article}
\usepackage[dvips]{graphicx}
%Barcode macro
%% for Code 128, Font im Paket  ctan:fonts/barcodes/willadt
\font\fntcxx=wlc128 scaled \magstep3
\def\CXXVIII{\bgroup\fntcxx\let\next\hexchar\next}
\def\hexchar#1#2{\if#1@\global\let\next\egroup\else\char"#1#2\fi\next}

\begin{document}

\section*{The barcode font}
Write into the preamble:
\begin{verbatim}
\font\fntcxx=wlc128 scaled \magstep3
\def\CXXVIII{\bgroup\fntcxx\let\next\hexchar\next}
\def\hexchar#1#2{\if#1@\global\let\next\egroup\else\char"#1#2\fi\next}
\end{verbatim}


%\maketitle
\section*{Testing the barcode}
%Defining our barcode
\begin{verbatim}
\def\barcode{\CXXVIII 68224152234F44450011216A@@}
\newsavebox\BBox
\sbox{\BBox}{\barcode}
\end{verbatim}


\def\barcode{\CXXVIII 68224152234F44450011216A@@}
\newsavebox\BBox
\sbox{\BBox}{\barcode}

%some debugging output
\begin{tabular}{ll}
Width:  &  \the\wd\BBox\\
Original Height: &   \the\ht\BBox\\
Depth:  &  \the\dp\BBox
\end{tabular}

\vspace{1cm}
\noindent
The original barcode:\\
\barcode\\

\noindent
The stretched barcode
\begin{verbatim}
\resizebox{\wd\BBox}{0.3\wd\BBox}{\usebox{\BBox}}
\end{verbatim}
\resizebox{\wd\BBox}{0.3\wd\BBox}{\usebox{\BBox}}

\end{document}