Struggle to capture good clear picture (8)
I believe the answer is:
'picture' is the definition.
(I know that vignette is a type of picture)
'struggle to capture good clear' is the wordplay.
'struggle' becomes 'vite' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'to capture' means one lot of letters goes inside another.
'good' becomes 'g' (abbreviation).
'clear' becomes 'net' (as in net profit).
'vite' placed around 'gnet' is 'VIGNETTE'.
(Other definitions for vignette that I've seen before include "Character sketch - word picture" , "Word-picture" , "Brief literary description" , "by way of illustration" , "Short description or character sketch" .)