'Mike & Yaël's Kill-White' is a Photoshop Filter that actively removes all white from an image (unlike the 'Multiply' blend mode).
However, this is not simple masking. Pixels that are "partly white" are altered so as to only remove the "white portion" - the altered pixel is now partly transparent instead of partly white.
I worked on this Filter with my good buddy Mike Simburger.
You can download the filter here: http://yaelmaritz.com/extras_killWhite.html