Picture one disadvantage (4)
I believe the answer is:
icon
'picture' is the definition.
(icon is a kind of picture)
'one disadvantage' is the wordplay.
'one' becomes 'i' (Roman numeral).
'disadvantage' becomes 'con' (as in pros and cons).
'i'+'con'='ICON'
(Other definitions for icon that I've seen before include "Adored person" , "Revered person or symbol" , "Saint's image" , "Sacred image or picture" , "Representative symbol or religious painting" .)