Working on image, a narcissist's problem (8)
I believe the answer is:
egomania
'narcissist's problem' is the definition.
(I've seen this in another clue)
'working on image a' is the wordplay.
'working' is an anagram indicator.
'on'+'image'='onimage'
'onimage' is an anagram of 'egomani'.
'egomani'+'a'='EGOMANIA'
(Other definitions for egomania that I've seen before include "Great self-absorption" , "Obsessive love of oneself" , "Extreme self-centredness" , "Obsessive self-interest" , "Obsessive self-concern" .)