they may do that by smudging, cloning and blurring a poser render, and painting in the hair.
the latter is difficult IMVHO, but there were guys in various poser sites who were noted for doing that
with fotos from porno sites, e.g. zemanova's.  one of them posted a tutorial after I said he was
just doing photocopies.  smudge, clone and blur until it doesn't look like a foto anymore.  that's
how I learnt doing cartoons at first, but I quit because it was unethical, not to mention getting
C&Ds. :lol: