In his new book, Constitution 3.0: Freedom and Technological Change, Jeffrey Rosen measures how endangered that right may become. He imagines a scenario where websites like Google and Facebook could "someday potentially post video from live surveillance cameras online — and then archive those videos in a database," which combined with facial recognition software, means police could easily identify most citizens. As unlikely a scenario as it is, according to Rosen, it's also not prohibited in the Constitution:

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