Disable Attachment Pages

add_action(

	'template_redirect',

	function () {

		global $post;

		if ( ! is_attachment() || ! isset( $post->post_parent ) || ! is_numeric( $post->post_parent ) ) {

			return;

		}

		// Does the attachment have a parent post?

		// If the post is trashed, fallback to redirect to homepage.

		if ( 0 !== $post->post_parent && 'trash' !== get_post_status( $post->post_parent ) ) {

			// Redirect to the attachment parent.

			wp_safe_redirect( get_permalink( $post->post_parent ), 301 );

		} else {

			// For attachment without a parent redirect to homepage.

			wp_safe_redirect( get_bloginfo( 'wpurl' ), 302 );

		}

		exit;

	},

	1

);