\documentclass{beamer}
% \usepackage[francais]{babel}
% \usepackage[latin9]{inputenc}
% \usepackage[T1]{fontenc}
% \usepackage{lmodern} 
\usepackage{pgf} 

\pgfdeclareimage{logo}{logoenst}
%[width=2cm]{logo}{logoenst}%

\begin{document}

  \pgfuseimage{logo}%
\end{document}
