Claim a gentleman is hiding a picture (5)
I believe the answer is:
image
'a picture' is the definition.
('image' can be a synonym of 'picture')
'claim a gentleman is hiding' is the wordplay.
'is hiding' indicates a hidden word.
'IMAGE' can be found hidden inside 'claim a gentleman'.
(Other definitions for image that I've seen before include "Picture; simile" , "Portrait, picture" , "Visible representation" , "Copy" , "Public impression" .)