poser in WordNet English dictionary

1. 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"
   model  poser 
   
2. a particularly difficult or baffling question or problem
   poser  stumper  toughie  sticker 
   
3. a person who habitually pretends to be something he is not
   poseur  poser