You can make a screenshot of the QR code and scan the picture through the the QR scanner.
Take a look here:
https://www.quora.com/How-can-you-scan-a-QR-code-that-appears-on-your-phone-browser-news-feed-or-email-application
One such app is QR Code Reader by Scan.
Here is what you will need to do:
1. Take a screenshot of the QR Code you’ve seen online and save it to your phone’s gallery
2. Download the QR Code Reader by Scan app on your smartphone
3. Open the app and tap on the option that redirects you to your phone’s gallery
4. Select the image you wish to scan
5. The app will scan the QR Code and show you the information linked in the QR Code on your smartphone
You can download the QR Code Reader by Scan app here for iOS and Android.
Also read: List of smartphones and apps with inbuilt QR Code reader
Hope this is helpful.