\documentclass{standalone}
\usepackage{graphicx}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
\node {\includegraphics[scale=0.5]{c2YtW}};
\node [fill=white,anchor=north east, inner sep=2.5pt, outer sep=2.6pt] at (current bounding box.north) {$\mathbf{n}$};
\end{tikzpicture}
\end{document}