Hi,
this may be stupid, but:
If I add crop marks, I have small lines extend beyond the image corners. But as soon as I cut one side of the image, I also cut the perpendicular crop marks away, so I'm blind when I come to cropping the other dimension.
The only solution that I see, would be crop marks extending "inside" the image in form of a "+" sign. Or am I completely missing the obvious here?