Turning off and on images in figures

You can either give the draft flag to the documentclass which has other implications as it gives the draft option to packages called (although some of them may ignore it).

Alternatively, calling the graphicx package with the draft option should just do what you want.

\documentclass[draft]{article}

or

\usepackage[draft]{graphicx}

If however, while in draft mode you want to see one of the graphics without adding them all in the output, you can unset the draft mode on a per file basis by setting draft to false as follows:

\includegraphics[draft=false]{image.pdf}

You can use the package draftfigure to get the same result and modify the display of the switched off figure:

\documentclass{article}

\usepackage{graphicx}
\usepackage[allfiguresdraft]{draftfigure}
\begin{document}
\includegraphics[width=50pt]{example-image-a}

\includegraphics[draft=false,width=50pt]{example-image-b}

\setdf{content={This figure is switched off.}}
\includegraphics[width=50pt]{example-image-c}

\end{document}