It's accurate enough that TV viewers might find the supplementary content Google sends useful. Nicole Kidman fans, for instance, might enjoy knowing what dress she's wearing on a broadcast of "Extra!" or where they can buy a similar outfit. Or ads for Cooper Minis might appear whenever the car showed up in a TV rebroadcast of The Italian Job.

All of this would work only if someone first manually notated what is onscreen at any given moment in a broadcast. With the volume of TV programming broadcast every day, that would be a tedious job. But in some cases it could be worthwhile for Google and advertisers, Fink says. "Say I'm an advertiser, and I would like a link to my website to appear with a specific episode of Seinfeld. We could open each moment of audio to a bidding process. The Google model of advertisers bidding for related words on Web pages, which has proved to be very successful online, could be carried over."

And the information Google sends doesn't have to be one-way -- it could also invite viewers watching the same program simultaneously to join a chat room, and administer surveys.

When word of the research first appeared in the media, some bloggers and other technology watchers reacted with horror; many assumed that the background conversation picked up by the microphone in Google's system would be uploaded to Google. But the technology makes it impractical; at four bytes, the fingerprints don't contain enough information to reconstruct the original sounds in a room. "Some people did get the impression that we had an open microphone that was going to listen in on them," says Norvig. "Clearly, that was not what we were doing. We are transmitting a key that can be matched but not reversed. That said, users are giving up some information -- and that's something they have to decide about."

Whether users could adapt to this new form of monitoring is uncertain. But the revenue opportunities are clear -- if the system works, that is. "It's a devilishly clever way to bridge those old and new media technologies," says Michael McGuire, an online media analyst at Gartner Research. But everything would depend on how accurately Google could match audio segments, he says. "You could imagine that if they were just a little bit off, it would drive you insane, in terms of the type of advertising you're seeing. And if it was far removed from what you were watching, you'd be jarred and maybe angry."

Fink's team is working on making the false-positive rate even lower -- so users don't get Doritos ads with their Masterpiece Theatre. But there's another challenge, notes McGuire: how to divide the attention of the viewer. "Presumably, broadcasters and advertisers wouldn't want anything so absorbing on the computer that it pulls viewers away from the actual broadcast. And even though the crowd that surfs the Web while they watch TV already knows how to multitask, they might ignore or block the online media stream if it starts to get too obtrusive. So [Google] would have to find a balance between information overload and effective advertising."