Making the background of blocks transparent

[Marie-Régine]

Hello,

I need to add a watermark to my beamer slides. Using a background
image works well, except that it doesn't shine through blocks when
they are "rounded". I suspect the issue may be in beamerbaseboxes, but
I do not understand the code, so I can't fix the problem :-( Anybody
have a hint for me?

MR


\documentclass{beamer}
\usetheme{Goettingen}

\setbeamertemplate{items}[ball]
\setbeamertemplate{blocks}[rounded][shadow=true]
% \setbeamertemplate{blocks}[shadow=true] % Works ok

\usepackage{graphicx}
\usebackgroundtemplate{\includegraphics[width=\linewidth]{draft}}

\begin{document}

\begin{frame}
Lorem ipsum dolor sit amet, consectetur adipisici elit, sed eiusmod
tempor incidunt ut labore et dolore magna aliqua. Ut enim ad minim
veniam, quis nostrud exercitation ullamco laboris nisi ut aliquid ex
ea commodi consequat.
\end{frame}

\begin{frame}
\begin{block}{}
Lorem ipsum dolor sit amet, consectetur adipisici elit, sed
eiusmod tempor incidunt ut labore et dolore magna aliqua. Ut enim ad
minim veniam, quis nostrud exercitation ullamco laboris nisi ut
aliquid ex ea commodi consequat.
\end{block}
\end{frame}

\end{document}