You can do the following. But as already mentioned in my comment, this seems like a bad idea to me. Are you really sure you want to do this?
\counterwithin{figure}{section}
\renewcommand\thefigure{\arabic{figure}}
To undo this effect you can use:
\counterwithout{figure}{section}
\renewcommand\thefigure{\thechapter.\arabic{figure}}
A complete example (which also shows the problematic behaviour of it):
\documentclass[]{report}
\usepackage[]{graphicx}
\counterwithin{figure}{section}
\renewcommand\thefigure{\arabic{figure}}
\begin{document}
\chapter{Foo}
\section{Bar}
\begin{figure}% >>>
\centering
\includegraphics{example-image-duck}%
\caption
{%
duck1%
\label{fig:duck1}%
}%
\end{figure}% <<<
\section{Baz}
\begin{figure}% >>>
\centering
\includegraphics{example-image-duck}%
\caption
{%
duck2%
\label{fig:duck2}%
}%
\end{figure}% <<<
\end{document}