One magazine that is including new picture (7)
I believe the answer is:
imagine
'picture' is the definition.
(picture can mean to visualise or imagine)
'one magazine that is including new' is the wordplay.
'one' becomes 'i' (Roman numeral).
'magazine' becomes 'mag' (abbreviation for magazine).
'that is' becomes 'ie' (short for Latin 'id est', 'that is').
'including' means one lot of letters goes inside another.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'ie' enclosing 'n' is 'ine'.
'i'+'mag'+'ine'='IMAGINE'
(Other definitions for imagine that I've seen before include "Suspect" , "See something that doesn't exist" , "Classic Lennon song" , "Reckon" , "Devise" .)