documentclass{article}

usepackage{caption}

usepackage{graphicx}

begin{document}

begin{figure}[h!]
centering
includegraphics[height=2cm]{figure}
caption{Une figure.}
end{figure}

begin{figure}[h!]
centering
includegraphics[height=2cm]{figure1}
captionsetup{labelformat=empty}
caption{Une figure.}
end{figure}

end{document}

documentclass{article}
usepackage{caption}
usepackage[demo]{graphicx}
begin{document}
begin{figure}[ht]
centering
includegraphics{figure1}
caption*{Caption.}
end{figure}
end{document}

documentclass{article}
usepackage{graphicx}
begin{document}
begin{figure}
  centering
  includegraphics[width=0.5textwidth]{Fig_test.png}
  caption{This with float name and number}
end{figure}
begin{figure}
  centering
  includegraphics[width=0.5textwidth]{Fig_test.png}par
  This with just the caption
end{figure}
end{document}