\documentclass[]{article}
\usepackage{graphicx}
\begin{document}
\section{A picture}
Here is a picture: natural size, fixed height, stretched:
\includegraphics{opensource-jitb.jpg}
\includegraphics[height=3cm]{opensource-jitb.jpg}
\includegraphics[height=2cm,width=6cm]{opensource-jitb.jpg}
\end{document}
|