wordpress网站的默认缩略图

I'm trying to modify my custom wp theme and add related post block. I want to add default thumbnail for posts which doesn't have it. Below code is working fine but i can't archive how to add default img.

$args = array( 'numberposts' => '4','post__not_in' => array($post->ID));
$recent_posts = wp_get_recent_posts($args);
foreach( $recent_posts as $recent ) {
    if($recent['post_status']=="publish") {
      if ( has_post_thumbnail($recent["ID"])) {
        echo '<div><a href="' . get_permalink($recent["ID"]) . '" title="Look '.esc_attr($recent["post_title"]).'" >' .   get_the_post_thumbnail($recent["ID"], 'thumbnail'). $recent["post_title"].'</a></div> ';
        } else {
            echo '<div><a href="' . get_permalink($recent["ID"]) . '" title="Look '.esc_attr($recent["post_title"]).'" >' .   $recent["post_title"].'</a></div>';
        }
    }
} 

In order to print the default thumbnail if the posts featured image is not found you have to print the default image that you have in your images folder.

<?php if ( has_post_thumbnail() ) {
the_post_thumbnail();
} else { ?>
<img src="<?php bloginfo('template_directory'); ?>/images/default-thumb-img.png"
alt="<?php the_title(); ?>" />
<?php } ?>

What the above code does?

It checks whether the post has thumbnails, if not it assigns the default-thumb-img.png ( Change it to your image name) as per your requirement.

my solution is just hardcode absolute link to default thumbnail

$args = array( 'numberposts' => '4','post__not_in' => array($post->ID));
                    $recent_posts = wp_get_recent_posts($args);
                    foreach( $recent_posts as $recent ){
                        if($recent['post_status']=="publish") {
                            if ( has_post_thumbnail($recent["ID"])) {
                                echo '<div class="col-md-3 col-lg-3"><div class="recent-post-holder"><a href="' . get_permalink($recent["ID"]) . '" title="Look '.esc_attr($recent["post_title"]).'" >' .   get_the_post_thumbnail($recent["ID"], 'thumbnail'). $recent["post_title"].'</a></div></div> ';
                            } else {
                                echo '<div class="col-md-3 col-lg-3"><div class="recent-post-holder"><a href="' . get_permalink($recent["ID"]) . '" title="Look '.esc_attr($recent["post_title"]).'" >' .   "<img src='/*add link here*/'>". $recent["post_title"].'</a></div></div>';
                            }
                        }
                    }