\documentclass{book}
\usepackage{tikz,graphicx}
\usepackage[a4paper,margin=1in]{geometry}
\usepackage{xepersian}
\settextfont{Parisa}
\begin{document}
    \centering  
    \begin{tikzpicture}[remember picture,overlay]
    %\setRTL
    \shade [top color=red,bottom color=blue] (current page.south west) rectangle (current page.north east); 
  \end{tikzpicture}
  
\begin{center}
\includegraphics[scale=.4]{ostad.jpg}
\end{center}
  \end{document}