Copy that’s all over publication (5)
I believe the answer is:
image
'copy' is the definition.
(an image might be a copy of something else)
'that's all over publication' is the wordplay.
'that's' becomes 'ie'.
'all over' indicates putting letters inside.
'publication' becomes 'mag' (abbreviation for magazine).
'ie' enclosing 'mag' is 'IMAGE'.
(Other definitions for image that I've seen before include "Figure (of speech?)" , "Mental picture; metaphor" , "Effigy, icon" , "Simulacrum" , "Likeness, might be spitting" .)