alt Hacker NewsBTP say [0] that "the images and biometric data of those who don’t cause an alert are automatically and immediately deleted." - if that's true, they shouldn't be able to tell that it's the same faces being scanned multiple times so it has to be 500k total scans rather than, say, 500k unique faces across 2 million scans
[0] https://www.btp.police.uk/police-forces/british-transport-po...
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cortesoft • yesterday at 3:40 PM
You could still delete while maintaining the ability to tell if a face has been seen before, by using some fingerprinting + one way hash function
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They're being very specific about images and biometric data, and they're weaseling those words for a reason. If they deleted all data about such scans, they'd say that.
To do the lookup they're still hitting a database somewhere to know you aren't a concern, which is prime time to log that you were seen, when, and where. Then your "images and biometric data" can be "immediately deleted" since they've gotten anything else they want now.
This is just a theory, but I bet I'm not far off.