Voici une solution.
solution avec le module `caption`
\documentclass[english,a4paper,12pt]{article}
\usepackage{lmodern}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{babel}
\makeatletter
\renewcommand\@makecaption[2]{%
\vskip\abovecaptionskip
\sbox\@tempboxa{#2}%
\ifdim \wd\@tempboxa >\hsize
#2\par
\else
\global \@minipagefalse
\hb@xt@\hsize{\hfil\box\@tempboxa\hfil}%
\fi
\vskip\belowcaptionskip}
\makeatother
\usepackage{caption}
\captionsetup[figure]{font={small, sf},labelformat=empty}
%ou
%\captionsetup{font={small, sf},labelformat=empty}
\begin{document}
\begin{figure}
\centering
\rule{3cm}{2cm}
\caption{Image Image Image Image}
\rule{3cm}{2cm}
\end{figure}
\end{document}
ou avec `caption`
\documentclass[english,a4paper,12pt]{article}
\usepackage{lmodern}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{babel}
\usepackage{caption}
\usepackage{caption}
\captionsetup{labelformat=empty}
\begin{document}
\begin{figure}
\begin{table}
\caption{Image Image Image Image}
\rule{3cm}{2cm}
\end{figure}
\end{document}
**Remarque** avec caption on peut écrire
\usepackage[font={small, sf},labelformat=empty]{caption}
ou
\usepackage{caption}
\captionsetup{font={small, sf},labelformat=empty}\centering
\begin{tabular}{|c|c|}
\hline
a & 1 \\
\hline
b & 2 \\
\hline
\end{tabular}
\end{table}
\end{document}
