Image row in Beamer

 Can use overlayarea and overlay specifications:

\documentclass{beamer}
\begin{document}
\begin{frame}
 \begin{enumerate}[<+->]
  \item Lion
  \item Cat
 \end{enumerate}
\vfill
\begin{overlayarea}{\textwidth}{2cm}
\only<1>{\centering\includegraphics[height=2cm]{ctanlion}\par}
\only<2>{\centering\includegraphics[height=2cm]{cat}\par}
\end{overlayarea}
\end{frame}
\end{document}

CTAN lion drawing by Duane Bibby.

I made a presentation using beamer, and at that time I use varblock environment, here one can write and include image in a certain location where ever you want.

By using varblock, I write 6 blocks and 3 of them was placed at the top and bottom blocks contains image. So the corresponding blocks contains the description of the image.

\begin{textblock}{}(1.1,2)
\begin{varblock}[5.5cm]{}
Any thing you can write OR\includegraphics{your picture}
\end{varblock}
\end{textblock}

To declare varblock, you have to write the following command before \begin{document}.

\newenvironment<>{varblock}[2][\textwidth]{%
  \setlength{\textwidth}{#1}
  \begin{actionenv}#3%
    \def\insertblocktitle{#2}%
    \par%
    \usebeamertemplate{block begin}}
  {\par%
    \usebeamertemplate{block end}%
  \end{actionenv}}