How to show related posts by category

In my gallery site i want to show other pictures under the current picture (in single post). I seen more codes but it i asks to specify the category, but i dont want want specify the category manually in the code I want the code itself to get the category ID or name.It would be much easier for me if i get full posts instead of post title so that I can display it as in home and category

The question has already been asked and the answer has been posted too,

How to display related posts from same category?

Add this code inside your single.php after a loop wherever you want to show related post,

<?php

$related = get_posts( array( 'category__in' => wp_get_post_categories($post->ID), 'numberposts' => 5, 'post__not_in' => array($post->ID) ) );
if( $related ) foreach( $related as $post ) {
setup_postdata($post); ?>
 <ul> 
        <li>
        <a href="https://wordpress.stackexchange.com/questions/41272/<?php the_permalink() ?>" rel="bookmark" title="<?php the_title(); ?>"><?php the_title(); ?></a>
            <?php the_content('Read the rest of this entry &raquo;'); ?>
        </li>
    </ul>   
<?php }
wp_reset_postdata(); ?>

It will display related post from the same category with the post excerpt and title ,
however if want this code to display just the title of related post then remove this line,

<?php the_content('Read the rest of this entry &raquo;'); ?>