list-featured-image.php

<?php

// Set featured images size
add_image_size( 'designsbynore-admin-post-featured-image', 125, 125, false );

// Add the column
function designsbynore_post_list_thumbnail_column($designsbynore_columns){
    $designsbynore_columns['designsbynore_thumb'] = __('Featured Image', 'textdomain' );
    return $designsbynore_columns;
}
add_filter('manage_posts_columns', 'designsbynore_post_list_thumbnail_column', 2);
add_filter('manage_pages_columns', 'designsbynore_post_list_thumbnail_column', 2);

// Get featured-thumbnail size post thumbnail and display it
function designsbynore_show_list_thumbnail_column($designsbynore_columns, $designsbynore_id){
    switch($designsbynore_columns){
        case 'designsbynore_thumb':
        if( function_exists('the_post_thumbnail') ) {
            echo the_post_thumbnail( 'designsbynore-admin-post-featured-image' );
        }
        else
            echo __( 'Your theme does not support featured images', 'textdomain' );
        break;
    }
}
add_action('manage_posts_custom_column', 'designsbynore_show_list_thumbnail_column', 5, 2);
add_action('manage_pages_custom_column', 'designsbynore_show_list_thumbnail_column', 5, 2);