\documentclass{article}\usepackage[pdftex]{graphicx}\usepackage{subfigure}
To reference subfigure do Figure ~\ref{fig:second}
\begin{figure} [htp] \begin{center} \subfigure[My First Figure]{\label{fig:first}\includegraphics[scale=0.30]{first.PNG}} \subfigure[My Second Figure]{\label{fig:second}\includegraphics[scale=0.30]{second.PNG}} \\ \end{center} \caption{MAVIS Interfaces} \label{fig:edge}\end{figure}