[Gimp-user] extract a reasonably dark image from its background?

[GimpDummy <forums gimpusers com>]

There is a new development which is more easily explained here on this screenshot: 
http://www.divshare.com/download/16734472-6d9        

This is the actual card size and appearance that I would be happy with:  
http://www.divshare.com/download/16727868-e64

but for some weird reason Vistaprint's specs won't accept it so I have to try and see if GIMP can make an 
image to Vistaprint's specifications as explained on the screenshot in the first link.

Thanks for all help so far.
Tom

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