Adding scalebars to images in LaTeX

LaTeXScaleBars.md

Scalebar with background

To change the backgroundcolor, adjust the scalebgcolor variable to use the desired color. Add the following code to your preamble:

\usepackage{tikz}
\usepackage[usenames, dvipsnames]{color}
\definecolor{scalebgcolor}{rgb}{0.08,0.52,0.80}

\newcommand{\scalebarbackground}[5][white]{
 \begin{tikzpicture}
  \node[anchor=south west,inner sep=0] (image) { #2 };
  \begin{scope}[x={(image.south east)},y={(image.north west)}]
   \fill [fill=scalebgcolor, fill opacity=0.5] (0.04,1.3em) rectangle (#5*#4/#3+0.04,0.1em);
   \draw [#1, line width=0.2em] (0.04,1.2em) -- node[below,inner sep=0.1em, font=\footnotesize] {\SI{#5}{\micro \meter}} (#5*#4/#3+0.04,1.2em);
  \end{scope}
 \end{tikzpicture}
}

Usage:

\scalebarbackground{\includegraphics[width=\linewidth]{image.png}}{1186}{9.887}{15} 

Scalebar without background

Add the following code to your preamble:

\usepackage{tikz}
\usepackage[usenames, dvipsnames]{color}

% Inserts a scale bar into an image
% Optional argument 1: the colour of the bar and text
% Argument 2: an \includegraphics command
% Argument 3: the real world width of the image
% Argument 4: the length of the scale bar in pixels
% Argument 5: the length of the scale bar in um
\newcommand{\scalebar}[5][white]{
 \begin{tikzpicture}
  \node[anchor=south west,inner sep=0] (image) { #2 };
  \begin{scope}[x={(image.south east)},y={(image.north west)}]
   \draw [#1, line width=0.2em] (0.04,1.2em) -- node[below,inner sep=0.1em, font=\footnotesize] {\SI{#5}{\micro \meter}} (#5*#4/#3+0.04,1.2em);
  \end{scope}
 \end{tikzpicture}
}

Usage:

\scalebar{\includegraphics[width=\linewidth]{image.png}}{1186}{9.887}{15} 

Thanks for the great example!
I've noticed a tiny issue with in it though - please take a look at this.
It would be very nice, if you would be able to fix your code here and in your tex.stackexchange.com answer, so that noone would have a chance to ran into this any more :).

Thank you @i3v, I've updated the code! 👍