Display a custom column for featured image in the admin for a custom post list

Before you use this code you need that have a custom post type ‘gallery’, or you can edit the code to match your existing custom post type.

You also need to have the theme support for the post thumbnails ‘gallery-thumb’ and its size, so Copy the below code and paste it in the functions.php file.

add_theme_support('post-thumbnails', array( 'post', 'gallery')); //Add this line if it does not exist
set_post_thumbnail_size(258, 112, true); //Add this line if it does not exist
add_image_size('gallery-thumb', 162, 122, true); //Add this line

Copy the below code and paste it at the bottom of your functions.php file.

add_filter('manage_gallery_posts_columns', 'gallery_thumbs_columns', 5);  
add_action('manage_gallery_posts_custom_column', 'gallery_thumbs_custom_columns', 5, 2);
  
function gallery_thumbs_columns($defaults){  
    $defaults['gallery_thumbs'] = __('Thumbnails');  
    return $defaults;  
}  
  
function gallery_thumbs_custom_columns($column_name, $id){  
    if($column_name === 'gallery_thumbs'){  
        echo the_post_thumbnail( 'gallery-thumb' );  
    }  
}