Model in picture, so pumped up (5)
I believe the answer is:
poser
'model' is the definition.
(I know that model can be written as poser)
'in picture so pumped up' is the wordplay.
'in' indicates a hidden word.
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'resop' is hidden in the letters of 'picture so pumped'.
'resop' backwards is 'POSER'.
(Other definitions for poser that I've seen before include "Problem to be solved" , "Difficult problem" , "Attitudiniser" , "Puzzling question about ropes" , "insincere?" .)