I can't beleive the first thought in their head would not be "This is a 15 year old girl! HELL NO you can't that picture!"
I think this is a case of the photographer having a great deal of prestige as an "artist" along with far more experience than the father in situations where he is talking models out of their clothes. "Let's just try this and if you don't like it I'll delete the picture." "Oh, this looks wonderful, you look so beautiful." Between the photographer's sales pitch and the father's knowledge of the context, he could easily have missed the fact that the pictures would look less classy out of context.
The trick is not to get into those situations, but an actress who needs regular photo shoots to keep her name recognition up and maintain her career is in a different situation than most kids, just as her father is in a different situation than most parents. Since her father has decided to allow an entertainment career, he needs to take her through these events. I think he really did make a careless error based on seeing the pictures in context. It wouldn't surprise me if he learns from this and doesn't make another mistake like that.
A final comment: I found the picture tacky but nowhere near pornographic. I wouldn't let my daughter pose like that, but I consider the pictures harmless or even a positive. Miss Cyrus may learn from this and follow a better path than most starlets, where an older girl might like receiving attention of a different type and consider it positive.
$$$$$$$$
i suspect that Ms. Cyrus' life is going to be in a total shambles by the time she is 30 (if she lives that long)......Wonder what good ole dad will say then.