Mastercard's pay-with-a-smile test is bound to rile privacy advocates (updated)

Amazon isn't the only one hoping you'll be willing to use biometrics to pay at the store. Mastercard has unveiled a Biometric Checkout Program that aims to set standards for paying with scans or gestures. The company hopes to make the purchase as simple as smiling for a camera or waving your hand in front of a reader — you wouldn't risk holding up the queue by reaching for your card, phone or watch.

The initiative would have you enroll either at the store or through an app. The potential standard is meant to accommodate shops of all sizes, and Mastercard is teaming with Fujitsu, NEC, Payface and other companies to establish baseline requirements for performance, privacy and security.

A pilot version is launching this week in Brazil, with Payface providing technology in five St Marche supermarkets across São Paulo. Customers will just have to smile to pay for their groceries. Tests are also planned for Asia and the Middle East, although Mastercard didn't share more details.

Biometric checkouts may be appreciated if you've ever fumbled for your wallet at the cash. As with other implementations, though, it's not clear if Mastercard will satisfy privacy concerns. Regardless of promises to protect your data, you're still trusting companies with photos and other sensitive body info. Many people aren't comfortable with that, and the Red Rocks Amphitheater even dropped Amazon palm scanning after a backlash from artists and activists worried about hacking and government surveillance. If Mastercard and its allies are going to establish a standard, they'll need to reassure shoppers that spies and fraudsters won't abuse body scans.

Update 5/17 3:58PM ET: Mastercard stressed that data would be converted into a digital template and encrypted, and that your face image stays on your device. This might not assuage everyone, but it's worth knowing if you're mainly concerned that someone else might have access to any photos.