Although Federation scanners have sufficient resolution to detect a ship at approximately 10 LY, this would obviously be insufficient to take a photo from outside the Romulan system.
In this case, the show script makes it clear that the "long-range scanner" Brackett is referring to is some kind of high resolution camera, presumably wielded by a Federation spy from some distance away:
A fuzzy, out-of-focus picture, with margins showing on screen, comes into frame -- something obviously taken on a very long lens. There are several blurred figures, none of them identifiable
ADMIRAL BRACKETT - Taken on Romulus, by long-range scanner. Computer, enhance image in section four-delta.