\subsection{Image sources}
\begin{frame}{Image sources}
    \begin{itemize}
        \item \href{http://commons.wikimedia.org/wiki/File:Sergey_Brin.JPG}{Sergey Brin} by enlewof
        \item \href{http://commons.wikimedia.org/wiki/File:Larry_Page_laughs.jpg}{Larry Page} by aweigend
    \end{itemize}
\end{frame}