gistfile1.aw

<?php
/**
 * If the post doesn't have a featured image set it to the first attached image
 * or a default if there are no images
 */
function pd_set_post_thumbnail( $post_id = null ) {
	if ( ! isset( $post_id ) )
		$post_id = get_the_ID();
	if ( has_post_thumbnail( $post_id ) )
		return true;

	$attachments_args = array(
		'post_parent' => $post_id,
		'post_type' => 'attachment',
		'numberposts' => 1,
		'post_mime_type' => 'image',
	);
	$default_args = array(
		'name' => 'pandodaily-default',
		'post_type' => 'attachment',
		'numberposts' => 1,
		'post_mime_type' => 'image',
	);
	if( ! $images = get_children( $attachments_args ) )
		$images = get_posts( $default_args );
	$image = array_pop( $images );
	return set_post_thumbnail( $post_id, $image->ID );
}