I have never used Gimp, so cannot say what options might work.
With Photoshop, it'd probably be a case of messing with selective colour, adding a bit of posterization and finishing with the stroke option.
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Captain Howdy,
Sat 28 Sep 2013, 9:35,
archived)
Happy endings, every time.
(
Captain Howdy,
Sat 28 Sep 2013, 10:22,
archived)
Vinegar strokes every time.
(
Jabberwoc misses D.R. and Quinch,
Sat 28 Sep 2013, 14:13,
archived)
I always finish with the stroke option
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mediocre ha ha ha, you're reading this,
Sat 28 Sep 2013, 10:15,
archived)