Drawing the anti-aliased lines in Gimp:
Steps:
1) Draw with "Pencil tool" lines on a transparent layer with whatever color and circle 03 (5x5) brush
2) Copy the layer as new image
3) Scale image 400%
4) Create new transparent layer
5) Select paintbrush tool (not pencil, but "paint smooth strokes using a brush")
6) Select "Circle fuzzy 17 (19x19)" brush
7) Select (0, 0, 128) color
8) Draw onto the new layer lines that match the ones copied
9) Duplicate layer
10) Scale layer 25%
11) Copy back to screenshot

(See also http://www.gimptalk.com/index.php?/topic/39124-antialiased-straight-lines/page__p__287171)

