So the customer set up an IT service with multiple servers to sync with yours so that both can sync to the ledger? How does that work in practice? Is someone also monitoring that nobody is doing a 50% attack? Are both parties present when something is inserted into the blockchain?

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) or a blockchain explorer like https://stellar.expert.

The great thing is that the data is stored on a distributed series of nodes, so no syncing is needed.

In some examples I've seen non-public ledgers, with X nodes run by the same company. And then they claim "we use blockchain so we're tamper-proof!"

Is your organization unusually susceptible to that kind of corruption? It seems like blockchain or no, the clients have to trust that you'll provide the service you agreed to and not cash their checks and disappear etc.

No.

But how are the many other people in the auto supply chain supposed to know that? With this solution, they don't have to trust our company, just the SHA256 hashing algorithm.

Math is easier to trust than a small startup.

Edit: To clarify, many of the people checking against the blockchain record are not our clients.