You probably don't need a decentralised, delay-tolerant network to send a photo to the person in front of you.
It's even very likely that this will be much less efficient than a direct Wi-Fi or Bluetooth connection or an AirDrop.
What would be the use case? Send the picture to someone at the other end of the lecture theatre? It's likely that there would be a phone network or Wi-Fi available.
A crisis or emergency situation where networks are down? There isn't much population density or movement to propagate the data.
This debate is not new, many teams have worked on wireless ad hoc networks, some with very encouraging results. The real problem is what the use cases are.
That's why I personally think that the use case should be related to travel, transport, sport or vehicle-to-vehicle communication. Situations involving movement and loss of connectivity.