You can backup QR in two formats Standard & Compact.
Standard QR can be scanned by any QR scanning device (like smartphone) & Compact QR needs specific software (eg. seedsigner software) to decode it because it uses binary instead of general alphanumeric or numeric data.
Compact QR is also easier to backup because it takes around 60% less area than Standard and it’s main purpose is to be easily transcribed by hand.
As Compact QR can’t be decoded easily it also adds an extra layer of security.
In this SeedQR cards (25×25 grid) 24 word seed can be stored as Compact QR format and 12 word seed can be stored as Standard QR format.