\begin{tikzpicture}[scale=0.45, every node/.style={transform shape}]

%\begin{tikzpicture}[scale=0.5, every node/.style={scale=0.5}]

% Bruit

\node[anchor=south west,inner sep=0] (image1) at (0,0) {\includegraphics[scale=1]{figures/correlation2d-2.png}};

\begin{scope}[x={(image1.south east)},y={(image1.north west)}]

\draw[red,ultra thick,dotted,rounded corners] (0.35,0.33) rectangle ++(0.15,0.2);

\end{scope}

% Smiley

\node[anchor=south west,inner sep=0] (image2) at (15,3.5) {\includegraphics[scale=0.24]{figures/correlation2d-1.png}};

% Image résultante

\node[anchor=south west,inner sep=0] (image3) at (20,0) {\includegraphics[scale=1]{figures/correlation2d-3.png}};

\begin{scope}[xshift=19.5cm]

\begin{scope}[x={(image3.south east)},y={(image3.north west)}]

\draw[red,ultra thick,rounded corners] (0.35,0.33) rectangle ++(0.15,0.2);

\end{scope}

\end{scope}

% Opérations

\node[scale=7] at (14.5,5) {$+$};

\node[scale=7] at (20,5) {$=$};

\node[scale=2] at (7,-1) {\bf Image de pixels aléatoires};

\node[scale=2] at (27,-1) {\bf Image avec le motif incrusté};

\end{tikzpicture}