I had nothing left but an image (4)
I believe the answer is:
idol
'an image' is the definition.
(I know that idol is a type of image)
'i had nothing left' is the wordplay.
'i had' becomes 'i'd' (I'd).
'nothing' becomes 'O' (looks like zero - 0).
'left' becomes 'l' (common abbreviation).
'id'+'o'+'l'='IDOL'
'but' acts as a link.
(Other definitions for idol that I've seen before include "Much-loved actor" , "Honoured figure" , "Who's greatly respected" , "something to be revered" , "Superstar; graven image" .)