The problem with more pairings is that you have a greater chance of identifying the right person because of their additional photos, but that gets offset by the

The problem with more pairings is that you have a greater chance of identifying the right person because of their additional photos, but that gets offset by the huge number of photos of everyone else in the database that you will now also get lots of "hits" on. For example, you might get lucky and 2 of the 3 test photos you have match well with 2 of the 5 database photos of the right person. But if you have enough people in the database, you're almost guaranteed to find some random person where all 3 of the test photos match quite well. So it often comes down to how you combine the results from the different test images. Do you take the max? Do you average them? etc. Each has different tradeoffs, and it's a topic under research at the moment ("image set recognition"), but I'd say there are no compelling results yet. Some personal devices might indeed be tuned for relatively fewer people, but these are precisely the cases that are the toughest: distinguishing between people in the same family, who're all going to look much more similar to each other than random people in a large database. But there are many scenarios where it might actually be distinguishing between 1000s of people. To take but one example, advertising. On the web, advertising is popular not just because it's "easy" and one of the few ways of successfully monetizing a site, but also because knowing more about a person allows for more targeted advertising which has a much bigger ROI. How would this translate to the "real world?" Personalization is clearly one of the ways to do this, and face recognition is ideal in many respects, given that it works from a distance, is non-invasive, and cheap to implement. (Obviously, there's a separate debate to be had about privacy and other issues, but I think it's hard to deny that many companies are interested in this.) I'm not sure that face recognition will be used for security purposes like house/car locks, just because it seems like other devices might get you better security sooner and cheaper (like RFID tags used in some car keys now, or some sort of ID from your phone).