As I've just found out while writing my presentation for BluePrint Durham, if you want to put a whole screen image into a LaTeX/Beamer presentation, you can't just centre it, as you end up with a fairly unwieldy left-margin. Unfortunately, the simplest solution that I can see is to use a tikzpicture frame.

Make sure you include \usepackage{tikz} in the preamble, and then for each image (per slide), use:

\begin{frame}[plain]
\begin{tikzpicture}[remember picture,overlay]
\node[at=(current page.center)] {
    \includegraphics[width=\paperwidth]{imagefilename}
         };
    \end{tikzpicture}
\end{frame}

(Solution courtesy of StackExchange, as ever.)