Wordpress Admin Thumbnails

wp-admin-thumbs.php

<?php
/**
 * Add Thumbnails To Admin & size them to max at 200px
 */
add_filter('manage_posts_columns', 'posts_columns', 5);
add_action('manage_posts_custom_column', 'posts_custom_columns', 5, 2);

/**
 * Add CPT Thumbs replace post-type with CPT, not neccesary if post thumbnails are supported for all types
 */
add_filter('manage_post-type_posts_columns', 'posts_columns', 5);
add_action('manage_post-type_posts_custom_column', 'posts_custom_columns', 5, 2);

function posts_columns($defaults){
    $defaults['riv_post_thumbs'] = __('Thumbs');
    return $defaults;
}

function posts_custom_columns($column_name, $id){
    if($column_name === 'riv_post_thumbs'){
		if( has_post_thumbnail() ) {
	    	echo the_post_thumbnail('medium');
	 	} else {
	    	_e('No Thumbnail For Post');
        }
        
	echo "
	<style>
	
	.column-riv_post_thumbs img{
		max-height: 300px;
		max-width: 250px;
	    }
	
	</style>
	";
    }
}
?>