I dont understand why they take naked picture..
+1,I also don't understand....
Most of these celebs will probably be in long-distance relationships and wont get much time to spend with each other due to filming commitments or whatever so this is probably one of the ways they can keep the relationship going or exiting. I know if I was in relationship with Jennifer Lawrence I wouldn't say no to her sending me the occasional titillating picture (pun intended).
Haha, true.
And even if they aren't in a LDR it's perfectly normal to take nude pictures of yourself, especially for women who are more self aware.
All of my ex's took nude pictures of themselves for various reasons and my current did so as well.