\documentclass{standalone}
\input{./tikzpreamble}
\begin{document}
    \begin{tikzpicture}
        \node[anchor=south west,inner sep=0] (image) at (0,0) {\includegraphics[width=\textwidth]{../pics/poweritv2_teststand_3.png}};
        \begin{scope}[x={(image.south east)},y={(image.north west)}]
            \draw[blue, fill=blue, fill opacity=.2, ultra thick, rounded corners] (.15, .25) rectangle (.08,.19);
            \draw[blue, fill=blue, fill opacity=.2, ultra thick, rounded corners] (.86, .71) rectangle (.94,.79);
            \draw[red, fill=red, fill opacity=.2, ultra thick, rounded corners] (.85, .24) rectangle (.93,.18);
            \draw[red, fill=red, fill opacity=.2, ultra thick, rounded corners] (.13, .71) rectangle (.06,.78);

            \draw[green, fill=green, fill opacity=.2, ultra thick, rounded corners] (.44, .85) rectangle (.64, .9);
            \draw[green, fill=green, fill opacity=.2, ultra thick, rounded corners] (.54, .12) rectangle (.35, .07);

            \draw[magenta, fill=magenta, fill opacity=.2, ultra thick, rounded corners] (.04, .8) rectangle (.14, .9);
        \end{scope}
    \end{tikzpicture}
\end{document}