Rising arches stolen in a photo (8)
I believe the answer is:
snapshot
'a photo' is the definition.
(I know that snapshot is a type of exposure)
'rising arches stolen' is the wordplay.
'rising' says the letters should be written backwards (going up in a down clue).
'arches' becomes 'spans' (I've seen this in another clue).
'stolen' becomes 'hot' (stolen goods are 'hot').
'spans' reversed gives 'snaps'.
'snaps'+'hot'='SNAPSHOT'
'in' acts as a link.
(Other definitions for snapshot that I've seen before include "print" , "Casual photograph" , "Quickly taken photograph" , "Quick photograph" , "Instant record of an event" .)