Something like this?

\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{positioning}
\usepackage{mwe}
\begin{document}
\begin{tikzpicture}
\node[anchor=south west,inner sep=0] (image) at (0,0) {\includegraphics[width=0.55\textwidth]{example-image}};
\node[anchor=south west,inner sep=0,right=5mm of image, draw=red, ultra thick] (image-b) {\includegraphics[width=0.55\textwidth]{example-image-a}};
\begin{scope}[x={(image.south east)},y={(image.north west)}]
\coordinate (A) at (0.65,0.65);
\coordinate (B) at (0.78,0.65);
\coordinate (C) at (0.78,0.75);
\coordinate (D) at (0.65,0.75);
\draw[red,ultra thick] (A) -- (B) -- (C) --(D) -- cycle;
\foreach \i/\j in {A/south west, B/south east, C/north east, D/north west}
\draw[red, ultra thick] (\i) -- (image-b.\j);
\end{scope}
\end{tikzpicture}
\end{document}
2nd version
To stop lines connecting corners at second image border, we need to find the intersection point between lines (B)--(image-b.south east) and (image-b.south west)--(image-b.north west) (and equivalent from C). This can be done with intersections cs.
\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{positioning,intersections}
\usepackage{mwe}
\begin{document}
\begin{tikzpicture}
\node[anchor=south west,inner sep=0] (image) at (0,0) {\includegraphics[width=0.55\textwidth]{example-image}};
\node[anchor=south west,inner sep=0,right=5mm of image, draw=red, ultra thick] (image-b) {\includegraphics[width=0.55\textwidth]{example-image-a}};
\begin{scope}[x={(image.south east)},y={(image.north west)}]
\coordinate (A) at (0.65,0.65);
\coordinate (B) at (0.78,0.65);
\coordinate (C) at (0.78,0.75);
\coordinate (D) at (0.65,0.75);
\draw[red,ultra thick] (A) -- (B) -- (C) --(D) -- cycle;
\end{scope}
\draw[red, ultra thick] (A) -- (image-b.south west);
\coordinate (aux) at (intersection cs:first line={(B)--(image-b.south east)}, second line={(image-b.south west)--(image-b.north west)});
\draw[red, ultra thick] (B) -- (aux);
\draw[red, dashed, ultra thick] (aux) -- (image-b.south east);
\coordinate (aux) at -(intersection cs:first line={(C)--(image-b.north east)}, second line={(image-b.south west)--(image-b.north west)});
\draw[red, ultra thick] (C) -- (aux);
\draw[red,dashed,ultra thick] (aux)--(image-b.north east);
\draw[red, ultra thick] (D) -- (image-b.north west);
\end{tikzpicture}
\end{document}
