The trusted source of time is the Stellar blockchain, and the last Bitcoin block hash, giving us a ~10 minute period wherein the photo must have been taken. Ess

The trusted source of time is the Stellar blockchain, and the last Bitcoin block hash, giving us a ~10 minute period wherein the photo must have been taken. Essentially, we abstract the time synchronization issue away from the photo taker to an external trusted source. The Bitcoin block hash cannot be known before it's calculated, and a new one is calculated every 10 minutes. Works great.