actually i worked for a company that provided path information (it's really really important) and privacy was absolutely key. they went to a lot of trouble in the design of the software so that, if they were ever compelled, even by a court order, to "identify individual X", they would LITERALLY be unable to comply and, to avoid contempt of court, would need to go to some technical lengths to explain why. they didn't use images (because they don't work) - instead they used GNURadio to do GSM passive decoding and signal-strength detection. and no, you *can't* track the person themselves, nor can you get their telephone number, nor can you decode their phone conversations, nor can you decode their SMS messages (not "and track 1000s of phones on affordable commodity off-the-shelf hardware at the same time"). they also track bluetooth and wifi, but again, the mac addresses are hashed (with salting) *before* being stored on disk. the reason for this kind of paranoia is really really simple: they ABSOLUTELY DO **NOT** wish to be involved in privacy and identification issues. it would destroy their reputation. so they made damn sure it simply could not happen, even if they were compelled by a court order.
anyway - first important thing: the definition of a "path" (and why it's critical). a "path" is, as the word suggests, the places that an individual goes to, and how they got there, how long it took, and how long and where they were stationary. key factors critical for shopping mall owners to be able to provide to their retailers: (1) how many unique shoppers went into *their* store (broken down by time and date is also helpful). (2) how long each unique shopper spent in their store. (3) also useful to know is where they went *before* going to another store. it's therefore necessary to weed out "passers-by", and duplicates (losing the path then picking it up as a *separate* person, repeatedly) is *especially* bad as it completely mucks up this all-important information that the retailers, it turns out, really really like to have once they know it's available.
think about it: this information is really, really important. in attracting retailers, without this equipment (or anything like it), the conversation is "come to our retail park, we have 6 million visitors a year". the retailer isn't interested in that. *with* the equipment (or anything like it), the conversation goes further, "and the unit we would like to interest you in gets 15,000 unique visitors per day if occupied by someone with your type of retail profile, especially because there's a macdonalds / starbucks within 100 / 50 metres and we know that that gets better numbers for you". *that's* powerful stuff, and it allows the shopping mall management to pick (and test, and research) interesting combinations of retailers that will make the whole mall a lively and attractive place to be, instead of being boring, half-empty of both retailers and customers (the other half being tired, stressed and exhausted), and doing a dis-service to everyone who bothers to go there.
so anyway i had to be up on the "competition" so to speak, because we frequently got questions coming in from clients being pitched the "visual tracking" technology.
first flaw in visual tracking technology: balloons, signs, pigeons, dogs, baby strollers - anything that moves in uncontrollable ways that is big enough to block people: you're hosed. pigeons etc. are fun because they randomly block out huge areas directly in front of the camera if they get close enough. even "other people" is enough to block "other people". even identifying "people" from children, babies, animals - this is hard enough as it is and requires enormous CPU resources... the number of people in some of these malls is *enormous* - tens to hundreds of thousands.
second flaw in visual tracking technology: it's intrusive. put a camera in a shopping mall and people automatically get edgy. it changes their "behaviour", which is precisely what you do not want. the last thing you want in a shopping mall is "edgy customers". some shopping centre managers *specifically* request suppliers of this kind of equipment *not* to walk around the store in clothing that is identified with "worker" or "engineer", and they prohibit the carrying clipboards, toolboxes and other stuff that said "annoying person to get away from immediately or be concerned about that they might be carrying a bomb etc. etc". they _really_ have to be careful about this kind of stuff. so: lots of big expensive high-resolution, high contrast ratio cameras with big zoom lenses: Baaaad.
third flaw in visual tracking technology: unless you have a hell of a lot of cameras and some extremely expensive CPUs, tracking upwards of 100,000 people in a single shopping centre means that moving from one camera to the next you lose continuity. once you lose continuity, that's it: it's "Game Over" for the whole concept of "one person". person goes into a toilet? you *really* don't want to go down that kind of tracking route. *but*.... person comes *out* of toilet, now you have a problem: you've lost continuity, and that means "oops, system thinks there's 2 people when there's actually only 1". now you're into lying about the number of people actually in the shopping centre. walk into a shop that has a complex layout (or doesn't want its customers intrusively tracked by cameras?), you lost the path. shops where people change their clothing? you lost the path. corridors with double fire-doors where you don't want people to have a camera staring them in the face no matter where they look? you lost the path. even that "80% success" figure is... it's just nowhere near enough: it genuinely has to be close to 100% to be useful. lose the path, you just lied to the retailer about the number of unique visitors, and you *can't do that*. "blur the face"?? wtf!! you just lost all the unique information needed to recover the path down the line, if it ever gets lost.
fourth flaw in visual tracking technology: drastic changes in lighting conditions. it turns out that to cope with sunlight changes at windows and doorways is drastically beyond both current camera technology *and* the CPU requirements of today's modern cluster computing, it's that CPU-intensive. and doorways are exactly where you really, really need to know about, because that's where the "path" of a unique shopper both begins and ends.
now the irony is that the subtleties of this are completely lost on many shopping mall managers. they *want* to be able to lie to the retailers that there are more people coming to the centre than there actually are, so the "whoops the reported numbers of unique shoppers are 6x higher than reality" is not a problem for such management, but for where it matters and you have retailers and mall management intelligent enough to understand, you *need* something different, and that's where the technology of the company i worked for comes into play, in a non-intrusive, non-privacy-invading fashion. and yes, it can be used for exactly the benefits described: emergency route planning and congestion reduction. just... without the privacy-invasion, thank you.
bottom line is: i really don't see how visual tracking is going to work out any time soon, especially given that face-blurring helps destroy critical information needed to rejoin paths if the tracking is ever lost, and especially given that the CPU usage is so enormous that you would need a supercomputer in the back office and a massively-upgraded power line to run it. no - don't expect visual tracking to be hitting a shopping mall near you in the immediate future.