Получите Templete Uri
<img src="<?php echo get_template_directory_uri(); ?>/images/logo.png" width="" height="" alt="" />
Black Heart
<img src="<?php echo get_template_directory_uri(); ?>/images/logo.png" width="" height="" alt="" />
// Get template directory example:
<img src="<?php echo get_template_directory_uri(); ?>/images/logo.png" />
// If you use child theme you will have to use another function:
<img src="<?php echo get_stylesheet_directory_uri(); ?>/images/logo.png" />
include( get_template_directory_uri() . '/includes/my_file.php' );