In fact, your US passport has that. Look for the biometric symbol on the front. It means there's a chip inside (not sure how to read off it) that includes your digitally signed identity details, including photo.
If you're willing to go the centralized route, then a minimalist ID card would just be a QR code that anyone can open and compare the official photo to you.
"Just a qrcode" would be a weird and inconvenient format.
Other countries (Estonia, Spain, Belgium) have smartcard IDs. You can add a qrcode to that, but the primary data store can be secured (and accessed and updated) in much the same way a regular smartcard is, you can access it from your home with a regular card reader and the relevant access application. And of course the size is completely standard. And you can add contactless support to it if desirable.
Plus the US already has experience with these types of IDs: DoD has issued 17 million Common Access Cards.
Whereas digital signing can be done in an offline, airtight system, as long as the public key is widely available.
https://play.google.com/store/apps/details?id=dexlab.eCL0WN&...