WP: Create A Custom Post-thumbnail Size

custom_post_thumb_size.php

<?php
/**
 * Location: functions.php
 *
 */

// drop in functions.php 
if ( function_exists( 'add_theme_support' ) ) { 
	add_theme_support( 'post-thumbnails' ); 
	add_theme_support( 'post-thumbnails', array('post', 'movie')); // include array of post_types (including registered ones)
	
	// more info: http://codex.wordpress.org/Function_Reference/add_image_size
	add_image_size( 
		'custom-size', // name
		279, // width 
		9999, // height
		true  // hard or soft crop
	);
}