Registering own thumbnails allows for creating additional images sizes, beyond those shipped with WordPress.
Your new image sizes should be registered inside app/Setup/thumbnails.php
file with add_image_size
function within after_setup_theme
action hook.
namespace Tonik\Theme\App\Structure;
function add_image_sizes()
{
add_image_size('custom-thumbnail', 800, 600, true);
}
add_action('after_setup_theme', 'Tonik\Theme\App\Structure\add_image_sizes');
Usage
Reference name of newly created image size when outputting images.
the_post_thumbnail('custom-thumbnail');