Une solution est d'utiliser l'option `valign=t` de l'extension [adjustbox](https://www.ctan.org/pkg/adjustbox).
\documentclass[10pt]{article}
\usepackage[showframe]{geometry}
\usepackage[table]{xcolor}
\usepackage{graphicx}
\usepackage[Export]{adjustbox}
\begin{document}
\sbox{0}{\parbox[t][256pt][t]{3.5cm}{\includegraphics[height=2.5cm,valign=t]{example-image-a} \\pli\\\vfill pli}}%
\setlength{\tabcolsep}{0pt}%
\setlength{\fboxsep}{0pt}%
\setlength{\fboxrule}{1pt}%
\noindent\begin{tabular}[t]{lcr}%
\cellcolor{black!25}\fbox{\usebox{0}}&\makebox[2mm]{}&%
\cellcolor{red!25}\fbox{\parbox[t][256pt][t]{5cm}{plu\\\vfill plu}}%
\end{tabular}%
\end{document}\end{document}
<img src="/upfiles/gre.png" style="width: 60%;"/>
