Inspired by Window Clippings, my preferred screenshot tool (which unfortunately crashes a lot under Windows 8 RTM), I wrote a small program for making image backgrounds transparent.
It comes with a command-line interface and a basic GUI (pictured above). The GUI supports dragging-and-dropping images, and you can switch the black and white images by right-clicking on either. The source code is included, along with a sample set of images.
The command-line syntax is: BackgroundRemover.exe imageout imageblack imagewhite
Thanks are owed to Ian Griffiths for the equations used to calculate transparency.
BackgroundRemover.7z
478,473 bytes; SHA-1: 002CF9C89B918951BBC7DECB9F9C1A8D53008E1F