Picture small boat (6)
I believe the answer is:
sketch
'picture' is the definition.
(I've seen this before)
'small boat' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'boat' becomes 'ketch' (ketch is a kind of sailing vessel).
's'+'ketch'='SKETCH'
(Other definitions for sketch that I've seen before include "'A rough, quick drawing (6)'" , "Short account" , "Rapid drawing - short play" , "Dead parrot featured in one" , "result of quick draw?" .)