Image on full slide in beamer package

This works:

\documentclass{beamer}
\title{test of full size graphic}
\usepackage{tikz}
\usetheme{AnnArbor}
\begin{document}
\begin{frame}
    \maketitle
    Notice the fancy presentation theme.\end{frame}
{ % all template changes are local to this group.
    \setbeamertemplate{navigation symbols}{}
    \begin{frame}[plain]
        \begin{tikzpicture}[remember picture,overlay]
            \node[at=(current page.center)] {
                \includegraphics[width=\paperwidth]{yourimage}
            };
        \end{tikzpicture}
     \end{frame}
}
\begin{frame}
    symbols should be back now\end{frame}
\end{document}

You have to run beamer twice to get the image centered in the right place. But if you have any other aux-file tricks (e.g., table of contents) you need to do that anyway.

If you're not already using tikz, you can save your image as a pdf and then use \includepdf(part of the pdfpages package). This will get you into trouble if you want to print your slides as an article or handout, though.