\documentclass{article}
\usepackage{expl3}
\usepackage{l3image}
\begin{document}
\ExplSyntaxOn
\mode_leave_vertical:
\hbox_set:Nn \l_tmpa_box { \image_include:n { example-image-a.pdf } }
\box_resize_to_wd:Nn \l_tmpa_box { \textwidth }
\box_set_trim:Nnnnn \l_tmpa_box { 0.5\textwidth } { 0pt } { 0pt } { 0pt }
\box_clip:N \l_tmpa_box
\box_use:N \l_tmpa_box
\end{document}