Set Featured Image Automatically using ACF

  1. Create a category image using ACF, field  = category_image
  2. This function will automatically (on saving the post or updating) look for the FIRST category assigned to it
  3. Then it will lookup that categories image and assign as a Featured Image to the Post
/** Sets the featured image on Single Posts based on the assigned Category*/function default_category_featured_image()


$featured_image_exists = has_post_thumbnail($post->ID);

if (!$featured_image_exists) 
// Get Category ID
// Get Image attached to the Category - we already have this
// Set Thumbanail

$yourcat = get_the_category($post->ID);
$category_ID = $yourcat[0]->term_id;
$categoryImage = get_field('category_image', 'category_'.$category_ID);
set_post_thumbnail($post->ID, $categoryImage["id"]);


add_action('save_post', 'default_category_featured_image');