In needgap, QR code is automatically generated here for each problem; so that the problem can be shared on web, chat for validation and those who view it on a computer can scan the QR via smartphone to get to the problem easily.
You can check out some of those problem QR at instagram - https://www.instagram.com/needgap/ shared separately by the admins here.
I agree that if someone sees that on a smartphone, the QR code can be scanned only after downloading the image or taking a screenshot and that's inducing some friction. For the scanner to automatically detect the QR on screen, it needs to take a screenshot and then process the image as it would do when the image is received from the camera. It's simple enough to implement, perhaps someone would if they agree with this need gap.