Set a fallback featured image with Genesis

functions.php

<?php
// Paste the code BELOW this line into your child theme functions.

/**
 * Set a fallback featured image with Genesis
 * 
 * @author Reasons to Use Genesis
 * @link http://reasonstousegenesis.com/default-featured-image/
 */
add_filter( 'genesis_get_image_default_args', 'rtug_fallback_featured_image' );
function rtug_fallback_featured_image( $defaults ) {
	$defaults[ 'fallback' ] = 200; // replace with your attachment ID
	return $defaults;
}