Ok, so try pasting this into functions.php file of your theme:
function add_title_attachment_link($link, $id = null) {
$id = intval( $id );
$_post = get_post( $id );
$post_title = esc_attr( $_post->post_title );
return str_replace('<a href', '<a title="'. $post_title .'" href', $link);
}
add_filter('wp_get_attachment_link', 'add_title_attachment_link', 10, 2);