\documentclass[12pt, a4paper]{letter} % Set the font size (10pt, 11pt and 12pt) and paper size
\usepackage{graphicx}
\usepackage{geometry}
\usepackage{eso-pic}
\usepackage[export]{adjustbox}
%\usepackage{tikz}
\usepackage{xcolor}
\definecolor{ustblue}{RGB}{0,57,116}
\geometry{
top=1cm,
bottom=2cm,
left=2cm,
right=2cm,
}
\newcommand\BackgroundPicture{
\put(0,0){
\parbox[b][\paperheight]{\paperwidth}{
\vfill
%\node[opacity=.06]
\centering\includegraphics[width=0.3\paperwidth,height=0.3\paperheight,keepaspectratio]{background.png}
\vfill
}}}
\AddToShipoutPicture{\BackgroundPicture}
\begin{document}
\begin{minipage}{0.5\textwidth}
\includegraphics[width=3in]{hkust_logo}\\
\end{minipage}
\hfill
\begin{minipage}{0.6\textwidth}\raggedright
\small{\textbf{\color{ustblue}Referee: }Name\\
\textbf{\color{ustblue}Address: }Room XXXX, Academic Building\\
\hphantom{AA}Department of XXX\\
\hphantom{AA}Hong Kong University of Science and Technology\\
\hphantom{AA}Clear Water Bay, Kowlon\\
\hphantom{AA}Hong Kong SAR, P. R. China\\
\textbf{\color{ustblue}Phone: }(852) XXXX-XXXX\\
\textbf{\color{ustblue}Email: }XXX@ust.hk }
\end{minipage}
\today
This student is so good! This student is so good!\\
This student is so good! This student is so good!\\
This student is so good!\\
This student is so good!\\
Please do not hesitate to contact me if you need me to provide more information.
Sincerely,
\includegraphics[width=2.5in]{signature}
XXX,\\
Professor in the Department of XXX,\\
Hong Kong University of Science and Technology\\
PhD in XXX, University of California, Berkeley
\end{document}
