It would have to perform with near-perfection: even if it turns out that it catches every single infringement except for video that is re-cut to 16:9 with letterboxing at 31fps, then all the pirates will just encode it that way and evade the filter, meaning that the system would generate an unacceptable level of false negatives.Link
In other words, all the money spent on the system would be for naught because it would fail to catch a significant proportion of pirates.
It would also have to be nearly perfect in regards to false positives - every time it misidentified a home movie of your kids' first steps or your gran's 85th birthday as Police Academy 29 or Star Wars: Episode 0, Jedi Teen Academy, your own right to use the Internet to communicate with your friends and family would be compromised - likewise unacceptable.
I write books. My latest is a YA science fiction novel called Homeland (it's the sequel to Little Brother). More books: Rapture of the Nerds (a novel, with Charlie Stross); With a Little Help (short stories); and The Great Big Beautiful Tomorrow (novella and nonfic). I speak all over the place and I tweet and tumble, too.