<?php
/*
 * Tests if any of a post's assigned categories are descendants of target categories
 *
 * @param int|array $cats The target categories. Integer ID or array of integer IDs
 * @param int|object $_post The post. Omit to test the current post in the Loop or main query
 * @return bool True if at least 1 of the post's categories is a descendant of any of the target categories
 * @see get_term_by() You can get a category by name or slug, then pass ID to this function
 * @uses get_term_children() Passes $cats
 * @uses in_category() Passes $_post (can be empty)
 * @version 2.7
 * @link http://codex.wordpress.org/Function_Reference/in_category#Testing_if_a_post_is_in_a_descendant_category
 */

if ( ! function_exists( 'post_is_in_descendant_category' ) ) {
	function post_is_in_descendant_category( $cats, $_post = null ) {
		foreach ( (array) $cats as $cat ) {
			// get_term_children() accepts integer ID only
			$descendants = get_term_children( (int) $cat, 'category' );
			if ( $descendants && in_category( $descendants, $_post ) )
				return true;
		}
		return false;
	}
}

function graphene_custom_header_image( $image ){
	if ( in_category(52) || post_is_in_descendant_category(52) ){
		/* The script to rotate through possible images here. */

		// Get the current category
		if ( $cat = get_query_var( 'cat' ) ){
			$cat = get_the_terms( $cat, 'category' );
			$cat = $cat[1]->slug;
		} else {
			global $post;
			$cat = get_the_category( $post->ID );
			$cat = $cat[0]->slug;
		}

		// The directory where the images reside
		$dir = get_stylesheet_directory() . '/images/custom-headers/' . $cat;

	  	if ( is_dir( $dir ) ){
			// Get all images from the $dir above
			$images = glob( $dir . "/*.jpg" );

			if ( $images ){
			   // Pick a random image
			   $key = array_rand( $images );

			   // Make sure the resulting image is assigned to the $image variable
			   $image = get_stylesheet_directory_uri() . "/images/custom-headers/$cat/" . basename( $images[$key] );
			}
		}
	}
   return $image;
}
add_filter( 'graphene_header_image', 'graphene_custom_header_image' );

?>