figure_annotations.tex

\documentclass{article}
\usepackage{geometry}
 \geometry{
 letterpaper,
 left=1in,
 right=1in,
 top=1in,
 bottom=1in,
 }
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}

\usepackage{amsmath,float}
\floatplacement{figure}{H}
\usepackage{hyperref}
\usepackage{tikz,pgfplots}
\pgfplotsset{compat=1.12}

\graphicspath{{./images/}}
\input{math_commands}

% used tikz libraries
\usetikzlibrary{patterns}
\usetikzlibrary{arrows}
\usetikzlibrary{calc}
\usetikzlibrary{intersections}
\usetikzlibrary{trees}
\usetikzlibrary{positioning}
\usetikzlibrary{arrows}
\usetikzlibrary{chains}
\usetikzlibrary{decorations.shapes}
\usetikzlibrary{decorations.pathreplacing}
\usetikzlibrary{decorations.pathmorphing}
\usetikzlibrary{decorations.markings}
\usetikzlibrary{shapes}
\usetikzlibrary{matrix}

\begin{document}

%=== MONTAGE ===%
\begin{figure}[!ht]
\centering

% style to add dot at the end of the line
\tikzset{
    o/.style={
        shorten >=#1,
        decoration={
            markings,
            mark={
                at position 1
                with {
                    \fill circle [radius=#1];
                }
            }
        },
        postaction=decorate
    },
    o/.default=1pt
}

\begin{tikzpicture}
\tikzstyle{every node}=[font=\small,color=blue]
\node at (0,0) {\includegraphics[width=\linewidth]{assembly}};

\draw (-5.2,2.5) node(a){Conditionnement};
\draw[o,color=red!70]  (a) -- +(0,-3);

\draw (-4,1.5) node(b){Contraction};
\draw[o,color=red!70]  (b) -- +(0.5,-1.7);

\draw (-2,1.5) node(b){Veine};
\draw[o,color=red!70]  (b) -- +(0.5,-1.2);

\draw (-0.5,2.8) node(b){Section d'essai};
\draw[o,color=red!70]  (b) -- +(1.2,-1.8);

\draw (2.5,3.5) node(b){Déversement};
\draw[o,color=red!70]  (b) -- +(1.4,-1);

\draw (2.2,-2.5) node(b){LDV};
\draw[o,color=red!70]  (b) -- +(1.9,3.35);

\draw (1,-3.5) node(b){Réservoir};
\draw[o,color=red!70]  (b) -- +(0.5,2.5);
\end{tikzpicture}
\end{figure}

% basic example to add letters to frames of a figure..
\begin{figure}
\centering
  \begin{tikzpicture}
	
	\draw (-8,-3.5) rectangle (8,4.5);
	
	%ns = [0 15 45 90 182 912500];
	\node at (-5.5,3.9) {\textit{(a)}\, 0 day};
	\node at (0, 3.9) {\textit{(b)}\, 1 month};
	\node at (5.8, 3.9) {\textit{(c)}\, 3 months};
	
	\node at (-5.5,-0.15) {\textit{(d)}\, 6 months};
	\node at (0,-0.15) {\textit{(e)}\, 1 year};
	\node at (5.8,-0.15) {\textit{(f)} \, 5 millennia};
\end{tikzpicture}	
\end{figure}

\end{document}