Over the last few months, I've been drawing collaborative portraits (using a basic app) with all my friends (in my iPhone address book). The Rules: Friend draws up to 3 strokes. Passes to Hsing (me), who builds on their drawing. Repeats back and forth until Friend declares "Stop." No erasing. End collaborative result gets assigned as their Contact image that pops up when they call or IM me.
It's been taking awhile to accumulate a critical mass of portraits, since I must physically see everyone (and not be forgetful when I do).
Most interesting has been the process -- Personalities didn't predictably draw concretely or abstractly; Varying ways to sidestep around the rules (Dan's is actually multiple pixel layers thick) not to mention varying degrees to which certain folks thought and tried to bend those rules; Each portrait unique with especially surprising differences btw close friends (favorite example Levi = one of Jay's best friends, Allysa = Jay's wife); Those who drew themselves vs depictions of what was happening with me in that moment vs. fantasies vs. whims of color. Larger Yearbook style group portrait of my portrait collection so far is viewable here.
4.18.10 UPDATE: On a personal level, its achieved what I had hoped for. A visualization of 1:1 combined bits of me + my Friends. And each time they call or text, a surprisingly clear memory of the moment when I drew with each person. Expanded version (larger version of below image) now viewable here

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