i dont really know why anyone would use this, but i guess its nice to know
start out with a picture, any picture
use mine if you wish ;]

first, duplicate the layer (Ctrl+J)
then, go to filter > blur > gaussian blur (top layer)
put in these these settings:
now, go to fliter > artistic > cutout
put in these settings:
now, your image should look like this:
set the layer style to overlay
your finished product should look something like this:
of course, it doesn't even come close to the quality of a real vector but... have fun :P
Tutorial Copyright helen! @ Blogring.