[Tex/LaTex] subfloat: how to position label to the left

Question

How can I make \subfloat put the labels to the left of the images? It seems it only supports "top" and "bottom". I am searching for a solution without using \tabular.
Thanks and regards, Jorge.

Example:

\documentclass{article}
\usepackage{subfig}
\usepackage{graphicx}
\begin{document}
\begin{figure}
\captionsetup[subfloat]{position=top}   % "position=left" is not supported!!! :(
\centering
\subfloat[]{\includegraphics[scale=0.5]{example-image-a}}
\vfill
\subfloat[]{\includegraphics[scale=0.5]{example-image-b}}
\end{figure}
\end{document}

Output (in red the location I'd like to achieve):

Answer 1

it is obtained by use of the environment \sidesubfloat from the package floatrow:

\documentclass{article}
\usepackage{floatrow}
\usepackage{graphicx}
\usepackage[label font=bf]{subfig}
\usepackage{caption}
\floatsetup[figure]{style=plain,subcapbesideposition=center}

\begin{document}
\begin{figure}
\centering
\sidesubfloat[]{\includegraphics[scale=0.5]{example-image-duck}}

\medskip
\sidesubfloat[]{\includegraphics[scale=0.5]{example-image-duck}}
\end{figure}
\end{document}