How to add, remove, replace a classes in image using the_post_thumbnail()? Let’s say we have this classes in image object. <img class="attachment-to-be-replace size-to-be-replace wp-post-image" src="https://www.anthonypagaycarbon.com/wp-content/uploads/image.jpg" alt="" width="800" height="600" > To replace the class name “to-be-replace”, copy this code to your functions.php add_filter( 'wp_get_attachment_image_attributes', function($attr){ $attr['class'] = str_replace( 'to-be-replace', 'hello-world', $attr['class'] ); return $attr; }); Output…