How can I control the vertical spacing of the parbox relative to the image?
\documentclass[12pt,a4paper]{article}
\usepackage[top=1in, bottom=1in, inner=1in, outer=1in]{geometry}
\usepackage[onehalfspacing]{setspace}
\usepackage[utf8]{inputenc}
\usepackage{ngerman}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{graphicx}
\usepackage{caption}
\captionsetup[figure]{font=normalsize,skip=10pt}
\usepackage[flushleft]{threeparttable}
\begin{document}
\begin{figure}[!htb]
\centering
\caption{}
\includegraphics[width=\textwidth,height=\textheight,keepaspectratio]{untitled.png}
\parbox{\textwidth}{\footnotesize Hallo}
\end{figure}
\end{document}

\parbox? – Werner Sep 23 '16 at 00:20\vspace{2cm}or whatever you need after the blank line brefore the parbox – David Carlisle Sep 23 '16 at 00:20