An image I'd behold in retrospect (4)
I believe the answer is:
idol
'an image' is the definition.
(idol is a kind of image)
'i'd behold in retrospect' is the wordplay.
'behold' becomes 'lo'.
'in retrospect' shows that the letters should be reversed in order.
'lo' written backwards gives 'ol'.
'id'+'ol'='IDOL'
(Other definitions for idol that I've seen before include "Sacred image" , "Graven image or greatly admired person" , "Favourite" , "Admired figure" , "Blue-eyed boy" .)