Auto Generate Image Alt Text

add_action( 'add_attachment', function( $attachment_id ) {

	if ( ! wp_attachment_is_image( $attachment_id ) ) {
		return;
	}

	$title = get_the_title( $attachment_id );
	$alt = preg_replace( '/[-_]+/', ' ', $title );
	update_post_meta( $attachment_id, '_wp_attachment_image_alt', sanitize_text_field( $alt ) );
} );