I worked out I needed to add quotes around the parameter.
echo get_avatar(get_the_author_meta('user_email'), '70', "'" . get_bloginfo('template_directory')."/images/default.png'");
I worked out I needed to add quotes around the parameter.
echo get_avatar(get_the_author_meta('user_email'), '70', "'" . get_bloginfo('template_directory')."/images/default.png'");