Line in picture, in a manner of speaking (8)
I believe the answer is:
drawling
'a manner of speaking' is the definition.
(I've seen this before)
'line in picture in' is the wordplay.
'line in' becomes 'l' (used when specifying particular lines from a poem. I am not sure about the 'in' bit.).
'picture' becomes 'drawing' (I've seen this before).
'in' is an insertion indicator.
'l' placed into 'drawing' is 'DRAWLING'.
Can you help me to learn more?
(Other definitions for drawling that I've seen before include "Prolonging vowel sounds in speech" , "manner of speaking" .)