\documentclass{standalone}
\usepackage{graphicx}
\usepackage{tabularx}
\def\quarterwidth{5cm}
\newcolumntype{C}[0]{>{\let\newline\\\arraybackslash\hspace{0pt}}m{\quarterwidth}}

\begin{document}
		\centering
		\begin{tabular}{C@{}C@{}}
						A & B \\
			\includegraphics[width=\quarterwidth]{model_cartoon.png}
			&
			\includegraphics[width=\quarterwidth]{model_coinsertables.png}
\\
						C & D \\
			\includegraphics[width=\quarterwidth]{ah_model_cartoon.png}
			&
			\includegraphics[width=\quarterwidth]{ah_coinsertables.png}
		\end{tabular}
\end{document}