"In any case if the subject of these photos is 13 then she is of legal age in about half of the world "
Dave, that is a load of rubbish. Spain, Mexico, Argentina and a few African countries is not half the world. Maybe if you had said 15 you would be right about legal age in half the world. And while the age of consent for sexual relations in parts of the world may be as low as 12 or 13 many countries have a higher minimum age for participation in pornography (including photos) or pornography is banned outright. For example in New South Wales I could legally have sex with a 16 year old girl, but if I was to have a pornographic image of her in my possession I could go to jail (and I recently heard a story of a 19 year old under police investigation in relation to a photo his 17 year old girlfriend emailed to him).
