"Cheating by manually creating signatures without actually meeting in person: is this an actual problem, and if so, how could it be fixed?" First naive thought

"Cheating by manually creating signatures without actually meeting in person: is this an actual problem, and if so, how could it be fixed?" First naive thought for a fix (if it is indeed a problem): - Keys managed by phone (assuming phone is trustable) - phone displays some signed fact as, for example, a QR code, for the 1st person 'exchanging' keys. - 2nd person in the WoT transaction takes a photo of 1st person holding QR display up next to face. - <insert CV/Facial Recognition/Mapping/Whatever Magic + QR code analysis> - repeat for 2nd party, with roles reversed.