Photoshop: I selected the Marquee tool and dragged out a thin vertical rectangle overlapping the first one. Immediately, the original rectangle is de-selected, and the new one becomes active. I then chose white as my foreground color, and used the Paint Bucket tool to fill it, essentially taking a "bite" out of my original. I have used the Magnifying Glass (or Zoom) Tool to enlarge the viewing area to 300% of original.