Hmm, I'm not quite sure what you're trying to ask. In the aforementioned case, the pickup time in known, so all that matters is that the photos are timestamped

Hmm, I'm not quite sure what you're trying to ask. In the aforementioned case, the pickup time in known, so all that matters is that the photos are timestamped before or at pickup time. We don't worry about 51% attacks because we use the Stellar blockchain, also used by Franklin Templeton investments and IBM and Keybase... The chance of a 51% attack going unnoticed is virtually zero. The ledger is public, and anyone can view the history of the ledger using Stellar's API (a hosted version is available at https://horizon.stellar.org https://horizon.stellar.org) or a blockchain explorer like https://stellar.expert https://stellar.expert. The great thing is that the data is stored on a distributed series of nodes, so no syncing is needed.