supp.tex

\documentclass[a4paper,12pt]{report}

%%% ELSA Toolbox %%%

% disable the draft mode
\usepackage{elsatoolbox}

%%% Main Content %%%

\begin{document}
\renewcommand{\thefigure}{S\arabic{figure}}
\begin{figure}
    \centering
    \includegraphics{example-image-a}
    \caption{An example image.}
    \label{fig:example}
\end{figure}
\end{document}