Artist Jorge Colombo has done New Yorker covers and more using an iPhone and the free open-source "finger painting" app Brushes. (Now Brushes 3. No idea what happened to Brushes 1 and 2.)
At the bottom of the page linked to are videos of 100 street sketches being drawn.
http://www.newyorker.com/online/blogs/culture/2012/01/cover-story-struck-by-the-light.html Watching the scene appear is an interesting illustration of technique.
Maybe my tastes are naïve, but I think his sense of composition has something that will appeal to street photographers.
Enjoy.
