Figure caption appears on the side instead below

Question

I am using beamer class to make a presentaation. I am using minipage to get 4 figures in 2 by 2 arrangement.

When I give captions to the figures 2 problems arise:

• The caption starts right from the figure instead of below
• Instead of decreasing the size of the figure the caption will be cut by the figure.
• I also get error: "\caption outside figure or table. \end{frame}"

\documentclass{beamer}
\usetheme{default}
\setbeamerfont{caption}{size=\footnotesize}
\begin{document}
  \begin{frame}
      \begin{columns}
          \column{0.5\textwidth}
          \begin{minipage}[c][0.4\textheight][c]{\linewidth}
              \centering
              \includegraphics[width=1\linewidth]{ETRM1042-epspdf-to}
              \caption{WT terminal voltage}
          \end{minipage}
          \begin{minipage}[c][0.4\textheight][c]{\linewidth}
              \centering
              \includegraphics[width=1\linewidth]{ITRM1042-epspdf-to}
              \caption{WT terminal current}
          \end{minipage}
          \column{0.5\textwidth}
          \begin{minipage}[c][0.4\textheight][c]{\linewidth}
                      \centering
                      \includegraphics[width=1\linewidth]{ETRM1042-epspdf-to}
                  \caption{Caption 3}
                  \end{minipage}
          \begin{minipage}[c][0.4\textheight][c]{\linewidth}
              \centering
              \includegraphics[width=1\linewidth]{VAACC-epspdf-to}
              \caption{previous Vterm angle}
          \end{minipage}
      \end{columns}
    \end{frame}
   \end{document}

Answer 1

Less complication you will have with the following approach:

\documentclass{beamer}
    \usepackage{graphicx}
    \usepackage{tabularx}

\begin{document}
\begin{figure}
\begin{frame}
    \begin{tabularx}{\textwidth}{*{2}{>{\centering\arraybackslash}X}}
\includegraphics[width=0.9\linewidth,height=24mm]{example-image-a}
\caption{WT terminal voltage}
    &   \includegraphics[width=\linewidth,height=24mm]{example-image-a}
        \caption{???}
        \\  % new row
\includegraphics[width=0.9\linewidth,height=24mm]{example-image-b}
\caption{WT terminal current}
    &   \includegraphics[width=\linewidth,height=24mm]{example-image-b}
        \caption{previous Vterm angle}
    \end{tabularx}
\end{figure}
\end{frame}
\end{document}

Of course, to see captions, your images show appropriate limit their heights.

Edit: To have numbered captions, you need to add in preamble \setbeamertemplate{caption}[numbered].

Addendum: As asked in comment, the "captions" without word "Figure" is easy to obtain -- just not use \caption{...} :-). Possible solution is demonstrated in MWE below.

\documentclass{beamer}
    \usetheme{default}
%----
    \usepackage{graphicx}
    \usepackage{tabularx}

\begin{document}
\begin{frame}
    \begin{tabularx}{\textwidth}{*{2}{>{\centering\arraybackslash}X}}
\includegraphics[width=0.9\linewidth,height=24mm]{example-image-a}\newline\footnotesize
WT terminal voltage
    &   \includegraphics[width=\linewidth,height=24mm]{example-image-a}\newline\footnotesize
        ???
        \\[1em]  % new row
\includegraphics[width=0.9\linewidth,height=24mm]{example-image-b}\newline\footnotesize
WT terminal current
    &   \includegraphics[width=\linewidth,height=24mm]{example-image-b}\newline\footnotesize
        previous Vterm angle
    \end{tabularx}
\end{frame}
\end{document}

which gives:

Answer 2

If I run your example I get

! LaTeX Error: \caption outside figure or table.

If you get an error it isn't really worth looking at the pdf output at all, teX tries to recover to error check more of the file but not to produce sensible output.

If I add tables as the error says the output looks OK to me:

\documentclass{beamer}
\usetheme{default}
\setbeamerfont{caption}{size=\footnotesize}
\begin{document}
  \begin{frame}
      \begin{columns}
          \column{0.5\textwidth}
          \begin{table}
              \centering
              \includegraphics[height=.3\textheight]{example-image}
              \caption{WT terminal voltage}
          \end{table}
          \begin{table}
              \centering
              \includegraphics[height=.3\textheight]{example-image-a}
              \caption{WT terminal current}
          \end{table}
          \column{0.5\textwidth}
          \begin{table}
                      \centering
                      \includegraphics[height=.3\textheight]{example-image-b}
                  \caption{Caption 3}
                  \end{table}
          \begin{table}
              \centering
              \includegraphics[height=.3\textheight]{example-image}
              \caption{previous Vterm angle}
          \end{table}
      \end{columns}
    \end{frame}
   \end{document}