/ Published in: PHP
The admin pages listing the site’s posts and pages come with various text columns (title, tags, categories, author and so on). In order to see what the featured images are, you have to visit each post or page individually. What I will show here, is how to get add a column with a reasonably sized thumbnail copy of the featured image. Please note that this only works for themes that support featured images.
URL: http://www.tcbarrett.com/2011/10/add-featured-image-thumbnail-to-wordpress-admin-columns/