<?php if(have_posts()): while(have_posts()): the_post();  ?>
   // show the single post and get the category of post
<?php endwhile;endif; ?>

if(isset($cats_arr) && !empty($cats_arr)){

        $args = array(
                'category__in' => $cats_arr,
                'posts_per_page'=>3,
                'post__not_in' => array( $post->ID ) );

        $the_query= new wp_query($args);

        if($the_query->have_posts()): while($the_query->have_posts()):
        $the_query->the_post();  ?>

 //// shoe same category post title and image
 <?php endwhile;endif ?>

 <?php comments_template();  ?>