Background Mistakes
Even though James tried to avoid using CGI as much as possible while making Titanic, there were times where he had no other choice. And as we all know, the more CGI a film has, the greater the risk of it having mistakes. For instance, see the woman in the top picture? The hat on her head was far too small to cast such a shadow.
And as for the pipe in the second and third picture, this was either a case of an identical set mix-up, or they rendered the CGI pipes inconsistently in two different shots. These were minor yet noticeable mistakes.