Picture of bridges being erected very popular (8)
I believe the answer is:
snapshot
'picture' is the definition.
(I know that snapshot is a type of picture)
'bridges being erected very popular' is the wordplay.
'bridges' becomes 'spans' ('span' can be a synonym of 'bridge').
'being erected' shows that the letters should be reversed in order (in a down clue, letters go up).
'very popular' becomes 'hot' (I've seen this before).
'spans' backwards is 'snaps'.
'snaps'+'hot'='SNAPSHOT'
'of' is the link.
(Other definitions for snapshot that I've seen before include "Informal photo" , "Informal photograph" , "Quick photograph" , "still taken quickly" , "Bit of camerawork" .)