\documentclass{article}
\usepackage{graphicx}

\begin{document}

    \begin{center}
    \begin{tabular}{cc}
    \includegraphics[width=.2\vsize]{chou3.pdf} & 
    \includegraphics[width=.2\vsize]{takao2.pdf} 
     \\
    \includegraphics[width=.2\vsize]{yamashita2.pdf} & 
    \includegraphics[width=.2\vsize]{hane2.pdf} 
    \end{tabular}
    \end{center}

\end{document}

\documentclass{article}
\usepackage{graphicx}
\usepackage{subfig}
\captionsetup[subfloat]{position=top}

\begin{document}

\begin{figure}
\begin{center}
    \begin{tabular}{ccc}
    \subfloat[Cho U (Zhang Xu)]{\includegraphics[height=.2\vsize]{chou3.pdf}\label{cho}} &
    \subfloat[Shinji Takao]{\includegraphics[height=.2\vsize]{takao2.pdf}\label{tak}} 
     \\
    \subfloat[Keigo Yamashita]{\includegraphics[height=.2\vsize]{yamashita2.pdf}\label{yam}} &
    \subfloat[Naoki Hane]{\includegraphics[height=.2\vsize]{hane2.pdf}\label{han}} 
    \end{tabular}

\caption{Heisei Four Emperors}
\label{emp}
\end{center}
\end{figure}

Figure \ref{emp} above ...

Figure \ref{yam} shows ...

Figure \subref{tak} is ...

\end{document}

\documentclass{article}

\usepackage{fancyhdr}
\pagestyle{fancy}
\fancyhead[L]{Top-left}
\fancyhead[C]{Top-center}
\fancyhead[R]{\thepage}
\fancyfoot[C]{deleted}

\begin{document}

contents.

\end{document}