A very simple macro for displaying centered images.
\documentclass{article}
\usepackage{simpleimage}
\begin{document}
\image[0.9]{filename}
\end{document}The first argument is the width as a fraction of \textwidth, the second is the filename.
Git clone or download the package and then symlink it into the appropriate place (different depending on os and laTeX distibution).
ln -s $PWD ~/Library/texmf/tex/latex/localAlternatively, put the simpleimage.sty file next to your document.