Nude picture: Is it important?

Well i think it was important as it was in the real story and as rose wanted a picture of herself in just wearing the pendant and nothing else, so it has to be there.

a movie is made to cater to all needs of all kinds of ppl so one scene is justified

There was no importance to that scene. Im sure you know that in the real Titanic there wasnt even a jack and rose love affair or even the blue diamond. It was all added to the movie for a better theme. But to answer your questions there truly was no reason for that scene. It was a good one though lol, but not important to the plot.