Picture that is on outside of magazine (5)
I believe the answer is:
image
'picture' is the definition.
('image' can be a synonym of 'picture')
'that is on outside of magazine' is the wordplay.
'that is' becomes 'ie' ('i.e.' can be a synonym of 'that is').
'on outside of' is an insertion indicator.
'magazine' becomes 'mag' (abbreviation for magazine).
'ie' going around 'mag' is 'IMAGE'.
(Other definitions for image that I've seen before include "Epitome" , "Mental picture; metaphor" , "Dead ringer" , "Likeness U symbol" , "Effigy, icon" .)