Is the image in a child theme? If so, use get_stylesheet_directory_uri()
instead as it will grab the child theme URL. get_template_directory_uri()
grabs the parent theme.
Depending on your PHP version adding a semicolon also might make a difference, and typically image src uses double quotes rather than single.
<img src="https://wordpress.stackexchange.com/questions/286570/<?php echo get_stylesheet_directory_uri(); ?>/img/no_results_found.png" />