Since the June 2019 update patch, Android phones running Android 8 (Oreo) and above can scan QR Codes using the phone's camera app. Apple phones have this camera functionality as well.
To scan a QR code, open the camera app, hold it towards the QR code for a few seconds for the camera to register the QR code. You may see a small banner, yellowed QR code (like mine, via the Moto G7), or similar graphic. Touch the QR code to open the link. From my Android phone:
Phones running Android 7 (Nougat) require a third party QR code app (see below).
Photo by Adactio
Creating a QR code is relatively easy, but there are a couple of things to keep in mind to make the best image possible:
Create codes via websites:
Create codes on your computer (freeware):
If you have Google Assistant on your phone then you have Google Lens on your phone. Google Lens lets you scan images, text, photos, and even QR codes.
To scan, simply open Google Assistant and click on the camera icon on the lower, right side of the assistant. Your phone's camera will activate and you can scan the QR code in question. You can also download Google Lens at https://lens.google.com/
2017: " iOS 11 Inbuilt QR Code Scanner: Apple Adds Feature to its Latest Update" https://scanova.io/blog/blog/2017/09/22/ios-11-inbuilt-qr-code-scanner-apple-adds-feature-latest-version/#.W6VsidW0IzY
QRreader beta (Chrome Browser)
Chrome extension: right-click (context) menu on QR code image and select "Read QR code from image"