Admin list column

<?php

// youngtimermagazine

add_filter('manage_posts_columns', 'posts_columns', 8);
add_action('manage_posts_custom_column', 'posts_custom_columns', 8, 5);

function posts_columns($defaults)
{
	$defaults['my_post_thumbs'] = __('Uitgelichte afbeelding');
	return $defaults;
}

function posts_custom_columns($column_name, $id)
{
	if ($column_name === 'my_post_thumbs') {
		echo the_post_thumbnail('admin-thumb');
	}
}