\documentclass[]{standalone}
\input{./tikzpreamble}
\begin{document}
    \begin{tikzpicture}
        \node[anchor=south west,inner sep=0] (image) at (0,0) {%
            \includegraphics{../../pitstop/20180901/calib_i48_s.pdf}
        };
        \begin{scope}[x={(image.south east)},y={(image.north west)}]
            \node[fill=white, draw=gray] at (.8, .52) {
                \includegraphics[width=.7\columnwidth]{mon48i.pdf}
            };
        \end{scope}
    \end{tikzpicture}
\end{document}