In today's security-conscious world, better access control-whether it's a company restricting entry into its building or a government monitoring entry into a country-has become a priority. One solution gaining popularity is biometrics, systems that use specific biological traits such as fingerprints or facial features to identify individuals. Face recognition is an especially appealing technique, because capturing an image of the face is simple and nonintrusive. But using face recognition for applications such as border control can require querying a database of thousands to millions of photos, which is time consuming and raises privacy concerns.

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