\documentclass[12pt,letterpaper]{article}
\usepackage{fullpage}
\usepackage{amssymb,amsthm}
\usepackage{subfigure}
\usepackage{graphicx}
\usepackage{doublespace}
\usepackage[latin1]{inputenc}
\spacing{1.5}
\begin{document}

\begin{figure}
 \centering
 \subfigure[Subgroup $\{e, b_1, b_2, r^2\}$]{
  \includegraphics{squarecoloring1.eps}}
 \subfigure[Subgroup $\{e, r, r^2, r^3\}$]{
  \includegraphics{squarecoloring2.eps}}
 \subfigure[Subgroup $\{e, d_1, d_2, r^2\}$]{
  \includegraphics{squarecoloring3.eps}}
 \caption{all dichromatic colorings of the square}
 \label{square_colorings}
\end{figure}
\end{document}
