Thematic Images on Post/Pages in Admin

gistfile1.php

// Adds Thumbnail to posts and pages back-end.

if ( !function_exists('snix_AddThumbColumn') && function_exists('add_theme_support') ) {
  // for post and page
	add_theme_support('post-thumbnails', array( 'post', 'page' ) );
	function snix_AddThumbColumn($cols) {
		$cols['thumbnail'] = __('Thumbnail');
		return $cols;
	}
	function snix_AddThumbValue($column_name, $post_id) {
			$width = (int) 35;
			$height = (int) 35;
			if ( 'thumbnail' == $column_name ) {
				// thumbnail of WP 2.9
				$thumbnail_id = get_post_meta( $post_id, '_thumbnail_id', true );
				// image from gallery
				$attachments = get_children( array('post_parent' => $post_id, 'post_type' => 'attachment', 'post_mime_type' => 'image') );
				if ($thumbnail_id)
					$thumb = wp_get_attachment_image( $thumbnail_id, array($width, $height), true );
				elseif ($attachments) {
					foreach ( $attachments as $attachment_id => $attachment ) {
						$thumb = wp_get_attachment_image( $attachment_id, array($width, $height), true );
					}
				}
					if ( isset($thumb) && $thumb ) {
						echo $thumb;
					} else {
						echo __('None');
					}
			}
	}
	// for posts
	add_filter( 'manage_posts_columns', 'snix_AddThumbColumn' );
	add_action( 'manage_posts_custom_column', 'snix_AddThumbValue', 10, 2 );
	// for pages
	add_filter( 'manage_pages_columns', 'snix_AddThumbColumn' );
	add_action( 'manage_pages_custom_column', 'snix_AddThumbValue', 10, 2 );