latex subfigure align top
begin{figure}
centering
begin{subfigure}[t]{0.45textwidth}
includegraphics[width=linewidth, height=20em]{example-image-a}
caption{taller image}
end{subfigure}
begin{subfigure}[t]{0.45textwidth}
includegraphics[width=linewidth, height=15em]{example-image-b}
caption{shorter image}
end{subfigure}
caption{two images}
end{figure}