I've cooked up a little video that shows the progression of one of my maps as the /locs are captured.
The blue crosses in the corners are registration marks that my mapper2.pl generates automatically when it parses the coordinates. They show the absolute maximum and minimum in-game coordinates for this map. When I paste the image into Photoshop, I use the crosses and those coordinates to generate the zonerect.
Although I capture some line in color, this is more as a reminder for me. I change them back to black before I do the texturing in Photoshop.