[cbzoiav]

It's not a case of can they be. It's a case of can they cheaply be.

The camera app on your smartphone likely searches for them by default. That means feeding at least 1-2 frames a second through it.

Basic pattern matching for the position markers is a rounding error overhead vs processing a video feed. Fancy computer vision is not - on lower end devices you may not have enough resources to do both and on higher end devices it'll still impact power usage.

[cwillu]

Low tech stupid solution: carry a sharpie.

[foota]

real CV programmers edit their QR codes with a sharpie

[nroets]

Approximately 10 years ago, I played with an Android app that takes the camera video input, looks for a Sudoku puzzle and then solves it. (AR Sudoku solver)

Detecting a QR code in real time should be possible on all devices by now...