For some reason, this reminds me of a news story I had posted here earlier - a 15 year old girl in Pittsburgh was arrested for "sexual abuse of children, possession of child pornography, and dissemination of child pornography". The child she abused - herself. Although, unlike your pictures, hers were sexually explicit, she didn't post them on a web page, and only emailed them to specific people she met online.
The news story is here:
Next question - if she masturbates, can she be arrested for child molestation?
I've wondered, if a girl takes sexual pictures of herself (or a similar situation for boy), but keeps them to herself until she turns 18 (or 21, or whatever arbitrary age is chosen for her land), are they still child pornography if she still wants them to exist? After all, she's old enough to give consent now. Do people have complete rights to their own selves? If not, who has the rights to a person that they do not?