\documentclass[a4paper,12pt]{article}
 

\usepackage{graphicx}
 \usepackage{xepersian}
\begin{document}
 
\begin{figure}[h!]
  \caption{A picture of a gull.}
  \centering
    \includegraphics[scale=.2]{a.pdf}
\end{figure}

 \begin{figure}[h!]
  \caption{A picture of a gull.}
  \centering
    \includegraphics[scale=.2]{b.pdf}
\end{figure}
\end{document}