Put Source under the table or figure[ usepackage[cappositon=top]{floatrow}

\documentclass{article}

\usepackage[capposition=top]{floatrow}

\begin{document}

\begin{figure}
% \centering% default with `floatrow`
\rule{1cm}{1cm}% placeholder for `\includegraphics`
\caption{A figure}
\floatfoot{A note}
\end{figure}

\end{document}