today I've tried WhatsApp Web, and I've seen there's a scanner for qrcode in whatsApp that scan only whatsapp's qr codes. How it is possible to recognize in an scan app my personal qr code? How whatsapp do? Any ideas? I want to try that in a personal app.
You don't have to identify the QR code but the contents of the QR code.
A QR is just a way to make text accessible to electronic devices. Once you have extracted the text contained on a QR code from your app, you only have to validate the text as with any other user input: run a regular expression, look it up on a database at your server...