Found picture at last in box (6)
I believe the answer is:
create
'found' is the definition.
(to found is to establish or create)
'picture at last in box' is the wordplay.
'picture at last' becomes 'e' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'in' is an insertion indicator.
'box' becomes 'crate' (crate is a kind of box).
'e' put into 'crate' is 'CREATE'.
Can you help me to learn more?
(Other definitions for create that I've seen before include "Build" , "institute" , "found" , "Appoint" , "Make or invent" .)