Mike and Yaël's KillWhite is a Photoshop Filter that actively removes all white from an image (unlike the 'Multiply' blend mode), perfectly leaving the rest of the image - whether the image is black-and-white or color.
However, this is not simple masking. Pixels that are partly transparent are altered so as to only remove the white portion. Shadows and gradients will remain in the image, only white is removed.

I worked on this Filter with my good buddy Mike Simburger.

Examples:

Tutorials:

• instantfundas.com: How to completely remove background from an image in Photoshop.
• addictivetips.com: White Background Removal With Kill White [Photoshop Plugin].
• 7DPRO.COM (via vimeo.com): Photoshop Tutorial: How to remove a subject from a white backdrop.

Download options:

Mike & Yaël's Kill-White (32bit Filter)
or
Mike & Yaël's Kill-White (Pixel Bender Version)

Versions Explanation:

The 32-bit Filter should be compatible with all 32bit PC versions of Photoshop that have filters. That would be the past 11 versions (3.0 though CS5!).

The Pixel Bender version makes use of Adobe's new (as of CS4) cross-program Filter system (works for both 64 or 32 bit versions). This version is much more accurate and generally has better results.

Installation Instructions for PC's:

32-bit Filter version:
Copy: KillWhite.8bf
To: ..Program Files\Adobe\Adobe Photoshop CS\Plug-ins\Filters

Pixel Bender version:
To get the Pixel Bender version working properly you need two things installed on your computer:

1. Adobe Pixel Bender !
   
   This is less of a problem in CS5 since it is allready installed as part of the suite,
   but if you're still not sure you can check to see if it's on your machins here:
   PixelBender 1.5 (CS4 on PC):
     ..Program Files\Adobe\Adobe Utilities\Pixel Bender Toolkit\
   PixelBender 2 (CS5 on PC):
     ..Program Files\Adobe\Adobe Utilities - CS5\Pixel Bender Toolkit 2\
2. Adobe Pixel Bender Plug-In for Adobe Photoshop.

Now that you made sure that everything's all hunky-dory, make sure Photoshop is open, go back to where you downloaded the KillWhite folder and double-click install_Killwhite.jsx.

Notes:

• There is a problem in CS5 wherein, in Photoshop, selecting the filter in the filter drop-down menu will crash the entire program. We are aware of the problem and are working on a fix.
  In the meantime you can still use the KillWhite by instantiating it through the Pixel Bender gallery:
  Open Photoshop > Filters > Pixel Bender Gallery (will open a new window) > Find the filter in the dropdown menu.
  
  
  Press OK (it'll go back to Photoshop).


• If you are a MAC user, the 32-bit Filter version will no work for you, and the Pixel Bender version will have to be installed . (We successfully tested the Pixel Bender version on a Macintosh running Photoshop CS4).

KillWhite by Mikeal Simburger and Yael Maritz is licensed under a 
Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.