NSFW) If a photoshopped picture of an underage celebrity's face is on the naked body of an over 18 person, would it be child porn?

I was searching for info about some actors/actresses when I came across a blog site with faked pictures of nude celebrities. Naturally being curious/intrigued I began looking more. Under comments for one of the photos of one followers of the blog requested pics of some girls who are only 16 or 17. This got me thinking if the girl being portrayed is under 18 but they use an of age body is this child porn? Just curious…