From WordNet (r) 2.0 (August 2003) [wn]:
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]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Poser \Pos"er\, n.
One who, or that which, puzzles; a difficult or inexplicable
question or fact. --Bacon.
[1913 Webster] Poseur
From Jargon File (4.4.4, 14 Aug 2003) [jargon]:
poser
n.
[from French poseur] A wannabee; not hacker slang, but used among
crackers, phreaks and warez d00dz. Not as negative as lamer or
leech. Probably derives from a similar usage among punk-rockers and
metalheads, putting down those who "talk the talk but don't walk the
walk".