On how to correctly put figures in your LaTeX document when you have two columns.

This post is biased for some parameters are chosen to correctly put figures in conference papers.

Assume that you want to include a picture in your two-column document. The basic way to do this is to use the figure environment along with the \includegraphics command from the graphicx package. The relevant parts of the code are detailed below.

\documentclass[conference]{IEEEtran}
% ...
\usepackage{graphicx}
% ...
\begin{document}
  % ...

  \begin{figure}[!ht]
    \center
    \includegraphics[width=\linewidth]{graphics/schema.jpg}
    \caption{\label{schema}My beautiful schema}
  \end{figure}

  As shown in figure \ref{schema}, this model allows...

  % ...
\end{document}

Now, if your picture is wide and it is not readable only in one column, you can make it span on the full width of the paper.

\documentclass[conference]{IEEEtran}
% ...
\usepackage{graphicx}
% ...
\begin{document}
  % ...

  \begin{figure*}[!ht]
    \center
    \includegraphics[width=\textwidth]{graphics/schema.jpg}
    \caption{\label{schema}My beautiful schema}
  \end{figure*}

  As shown in figure \ref{schema}, this model allows...

  % ...
\end{document}

There are actually only two differences. The figure* environment is used instead of figure, and the width of the included graphics is \textwidth instead of \linewidth.

If you want to adjust the size of your image, you can put a number in the length. A good way to do this is to write width=0.8\linewidth or width=0.8\textwidth for example, depending on your use case.