The wording next to the code matters more than the code
A bare square with “Scan me” underneath gets scanned by the curious and ignored by everyone else. Say what it does and who it is for — “Send us your photos from tonight” — and add the couple’s names. Guests scan things they understand the purpose of.
Placement is the other half. A code on the gift table is read once, by the person putting down the envelope. A code on every table number is in front of a seated guest for two hours, which is when people have their phones out, their drink down and nothing to do between courses.
Then say it out loud. One line from whoever is holding the microphone before the speeches — “the square on your table sends us your pictures” — often doubles the number of photos. The printed code is the reminder; the announcement is what gets people to act.