How to scan a a QR code that is on your screen?
Yes, you can do this without another device:


Take a screen shot of your screen and make sure the QR code is captured properly. Crop to the QR code in the screenshot and save the image file using Preview.
Open this image file in an app like Barcode Scanner and QR Code Reader. (Alternatively, you can upload the QR image file to an online QR code reader).
The app will decode the QR and provide you the data.