Proof of work is not needed, just a pool of time servers that you can make a quorum out of. We're working on exactly this on top of roughtime (https://roughtime.googlesource.com/roughtime) for a future version of QR Date (https://qrdate.org/)

Great discussions! Some thoughts:

First, there are multiple solutions to this problem, all need to be explored and many will have a part in the future. Bad actors will do everything they can to find a way around every solution.

Second, for the hashing approach, have a look at "Perceptual Hashing", it's a way to hash content like a an image, even if the resolution changes.

Where to store the hashes? A centralized server is probably fine, but there is always a risk of a bad actor exposing it somehow. A secure blockchain can work better. But if you go that route, might as well go with the most secure blockchain. POW is generally more secure than POS. And currently the most secure blockchain is Bitcoin. So one solution is to batch hashes together and write them with a Bitcoin transaction in some cadence.

-Ali