Posh British student in picture generally known (6)
I believe the answer is:
public
'generally known' is the definition.
(I've seen this before)
'posh british student in picture' is the wordplay.
'posh' becomes 'u' (abbreviation for upper-class - opposite to non-U).
'british' becomes 'b' (abbreviation e.g. in BBC).
'student' becomes 'L' (learner, as in L-plates for learner drivers).
'in' means one lot of letters goes inside another.
'picture' becomes 'pic' (short for picture).
'u'+'b'+'l'='ubl'
'ubl' put into 'pic' is 'PUBLIC'.
(Other definitions for public that I've seen before include "People in general" , "In open view" , "General - population" , "Relating to the general community" , "Unconcealed" .)