I have several images and I must put their names below them. Moreover, I need to give the name of the group of that images too (for example, "first layer", "second layer" ect as show below). I need to have something as shown in the figure below.
IMPORTANT: In my case, a group of images may contain more than one row. I mean, the "(a) first layer" may contain more than 3 images and hence can be a group of images in more than one row.
Two options:
Using some tabulars for each layer and the subcaption package:
The code:
\documentclass{article}
\usepackage{subcaption}
\usepackage{graphicx}
\begin{document}
\begin{figure}
\begin{minipage}{\linewidth}
\centering
\begin{tabular}{ccc}
\includegraphics[width=.28\linewidth,height=1cm]{example-image-a}
& \includegraphics[width=.28\linewidth,height=1cm]{example-image-b}
& \includegraphics[width=.28\linewidth,height=1cm]{example-image-c} \\
First image & Second image & Third image \\
\includegraphics[width=.28\linewidth,height=1cm]{example-image-a}
& \includegraphics[width=.28\linewidth,height=1cm]{example-image-b} \\
Fourth image & Fifth image &
\end{tabular}
\subcaption{First layer}
\end{minipage}\par\bigskip
\begin{minipage}{\linewidth}
\centering
\begin{tabular}{ccc}
\includegraphics[width=.28\linewidth,height=1cm]{example-image-a}
& \includegraphics[width=.28\linewidth,height=1cm]{example-image-b}
& \includegraphics[width=.28\linewidth,height=1cm]{example-image-c} \\
First image & Second image & Third image \\
\end{tabular}
\subcaption{Second layer}
\end{minipage}
\caption{a figure with some layers of subfigures each with its own name and each layer with a subcaption}
\end{figure}
\end{document}
Above I used a standard tabular with three c type columns; if the text below the images should span more than one line, you could use tabularx from the tabularx package and centered X columns, as the option below illustrates.
Since the OP is using subfig, the subcaption package cannot be used; here's an approach using the same idea as before, but with tabularx and the subfig package:
\documentclass{article}
\usepackage[caption=false]{subfig}
\usepackage{graphicx}
\usepackage{tabularx}
\newcolumntype{Y}{>{\centering\arraybackslash}X}
\begin{document}
\begin{figure}
\subfloat[First layer]{%
\begin{minipage}{\linewidth}
\centering
\begin{tabularx}{\linewidth}{YYY}
\includegraphics[width=\linewidth,height=1cm]{example-image-a}
& \includegraphics[width=\linewidth,height=1cm]{example-image-b}
& \includegraphics[width=\linewidth,height=1cm]{example-image-c} \\
First image & Second image & Third image \\
\includegraphics[width=\linewidth,height=1cm]{example-image-a}
& \includegraphics[width=\linewidth,height=1cm]{example-image-b} \\
Fourth image & Fifth image &
\end{tabularx}
\end{minipage}}\par\medskip
\subfloat[Second layer]{%
\begin{minipage}{\linewidth}
\centering
\begin{tabularx}{\linewidth}{YYY}
\includegraphics[width=\linewidth,height=1cm]{example-image-a}
& \includegraphics[width=\linewidth,height=1cm]{example-image-b}
& \includegraphics[width=\linewidth,height=1cm]{example-image-c} \\
First image & Second image & Third image \\
\end{tabularx}
\end{minipage}}
\caption{a figure with some layers of subfigures each with its own name and each layer with a subcaption}
\end{figure}
\end{document}
Undefined control sequence. \subcaption because I am already using \usepackage[caption = false]{subfig}
subfig instead.
\usepackage[caption = false]{subfig} and hence I cannot use \usepackage{subcaption} in combination to it
subfig package like this: \usepackage[caption=false,font=normalsize]{subfig}. The other option is to use something like \small First image & \small Second image... inside the table to reduce the font size for the image names.
You can have multiple rows, e.g. look at this example from ClassicThesis:
begin{figure}[bth]
\myfloatalign
\subfloat[Asia personas duo.]
{\includegraphics[width=.45\linewidth]{gfx/example_1}} \quad
\subfloat[Pan ma signo.]
{\label{fig:example-b}%
\includegraphics[width=.45\linewidth]{gfx/example_2}} \\
\subfloat[Methodicamente o uno.]
{\includegraphics[width=.45\linewidth]{gfx/example_3}} \quad
\subfloat[Titulo debitas.]
{\includegraphics[width=.45\linewidth]{gfx/example_4}}
\caption[Tu duo titulo debitas latente]{Tu duo titulo debitas
latente.}\label{fig:example}
\end{figure}
\newcommand{\myfloatalign}{\centering}