These are silk screens portraits generated by a program I wrote called Graffitizer.
It is based on an idea I wanted to develop by hand, but I ended up writing an algorithm to simulate the process I had in mind, and to do the tedious work for me.
An image is reconstructed by adapting basic graffiti elements ( arrows, bars, and other shapes ) to color areas.
This is done with a particle based algorithm, that spawns color sensitive particles that expand over areas based on the hue, luminosity, or distance in RGB space.
Once these areas are defined, an element from a library of pre drawn 'graffiti' elements is adapted to that area, finally generating a postscript file.
The output of the program is an eps that is then hatched in Adobe Illustrator using a custom Scriptographer script.