poser (
http://definr.com/poser)
n 1: a person who habitually pretends to be something he is not
[syn:
poseur]
2: a person who poses for a photographer or painter or
sculptor; "the president didn't have time to be a model so
the artist worked from photos" [syn:
model]
3: a particularly difficult or baffling question or problem
[syn:
stumper,
toughie,
sticker]