Here I use the feature of specifying a separate heading in the toc to add the graphic, via lap, if necessary.
\documentclass{article}
\usepackage{graphicx}
\begin{document}
\tableofcontents
\noindent\hrulefill
\section{Normal section}
\section[{\llap{\includegraphics[height=\baselineskip]{example-image}%
\kern20pt}Left of section number}]{Left of section number}
\section[{Right of title \includegraphics[height=\baselineskip]{example-image}}]%
{Right of title}
\section[{Right of page number\hfill\rlap{\kern20pt\includegraphics%
[height=\baselineskip]{example-image}}}]{Right of page number}
\end{document}

SUPPLEMENT
In response to comments about the use of \chapter
in the book
class, and vertical alignment of the image, I provide an additional MWE:
\documentclass[a4paper,openright]{book}
\usepackage{graphicx}
\DeclareRobustCommand\addimg[1]{\llap{\raisebox{-\dp\strutbox}%
{\includegraphics[height=\baselineskip]{#1} \kern20pt}}}
\begin{document}
\tableofcontents
\noindent\hrulefill
\chapter[\addimg{example-image}Left of section number]{Left of section number}
\chapter[\addimg{example-image}Machines d'audit et processus MCO et MCS]{Machines d'audit et processus MCO et MCS}
\end{document}
