Beans: set post default image.

functions.php

<?php
// Do not include the opening php tag if it is already included in your file.

add_action( 'beans_post_body', 'beans_child_default_post_image', 5 );

function beans_child_default_post_image() {

	// Stop here if the post has an image set.
	if ( has_post_thumbnail() )
		return;
		
	// You may use beans_edit_image() if you need to create multiple size on the fly.
		
	echo '<img src="' . get_stylesheet_directory_uri() . '/images/your-default-image.jpg" alt="">';
  
}