Code to Add Featured Image Column in WordPress All Post List

/* Featured Image Column All Posts List */
add_filter('manage_post_posts_columns', 'misha_featured_image_column');
function misha_featured_image_column( $column_array ) {
	$column_array = array_slice( $column_array, 0, 1, true )
	+ array('featured_image' => 'Featured Image') 
	+ array_slice( $column_array, 1, NULL, true );
	return $column_array;
}
add_action('manage_posts_custom_column', 'misha_render_the_column', 10, 2);
function misha_render_the_column( $column_name, $post_id ) {
	if( $column_name == 'featured_image' ) {
		if( has_post_thumbnail( $post_id ) ) {
			$thumb_id = get_post_thumbnail_id( $post_id );
			echo '<img data-id="' . $thumb_id . '" src="' . wp_get_attachment_url( $thumb_id ) . '" />';	
		} else {
				echo '<img data-id="-1" src="' . get_stylesheet_directory_uri() . '/placeholder.png" />';		
		}}}
add_action( 'admin_head', 'misha_custom_css' );
function misha_custom_css(){
	echo '<style>
		#featured_image{
			width:100px;
		}
		td.featured_image.column-featured_image img{
			max-width: 100%;
			height: auto;
		}
		#misha_featured_image .title{margin-top:10px;display:block;}
		#misha_featured_image a.misha_upload_featured_image{
			display:inline-block;
			margin:10px 0 0;
		}
		#misha_featured_image img{
			display:block;
			max-width:200px !important;
			height:auto;
		}
		#misha_featured_image .misha_remove_featured_image{
			display:none;
		}
	</style>';
}

Source: Rudrastyh

How do you know whether a Post has a Featured Image or not? The answer is simple. Just add a Featured Image Column in All Posts list. The above code adds a featured image thumbnail to the all posts list, making it easy for publishers.

Add the above code to your Child Theme’s functions.php. This generates a ‘Featured Image‘ column in the admin all posts list.