They legally can take a photo of you, sure. But they aren't just taking a photo from across the street. They are also: 1. "briefly" detaining you to make you

They legally can take a photo of you, sure. But they aren't just taking a photo from across the street. They are also: 1. "briefly" detaining you to make you face a camera and take of hats etc for the app to get a good enough shot. 2. arresting you if it doesn't correctly identify you 3. using protected characteristics to decide who needs to get scanned.