If only there were a method used daily in industry to move data back and forth from secure systems in a write-once fashion. Hear me out - you could construct some sort of polycarbonate disc that would contain a substrate. You could then permanently encode your data onto this substrate - so it couldn't be changed - with a "laser" perhaps. Then said disc could be read on another machine without worry of sneaky things hiding in your USB. On second thought that sounds way too complicated and I'd probably stick with the QR code-camera thing.