Automation of isolating image

This is an image of a man standing in a white space. [login to view URL] Most of the white space is already a 'pure white' that is RGB 255,255,255, however some of the space is not yet a pure white. I need some sort of software that make all of the white space a pure white. It can be a software that lives in the cloud or a software that runs on OS X 10.8.3. Or a photoshop plugin for photoshop CS5/6. Please give me your best price in your bid.