Is it a sin to take nude pictures of yourself?
If you were the only person to see those pictures, it would not be a sin. It would be no different than seeing yourself in a mirror. However, few people take pictures just for themselves. Sharing pictures of your naked self would be just as wrong as exposing yourself to other people. See: Is it a sin to hang out with no clothes on?
Another consideration is that images taken on a device rarely remain private. Eventually someone will discover them.