I only know of one crypto-currency backed by assets.
Problem with that is that you never know. There is lots coins gold backed. Stable coins are fiat backed. But do they have any Gold really. Do they have fiat stored somewhere? You dont know. So is really stupid idea to buy such coin. Buy USD or Gold not token baked by them.
Xaurum posted photos of their gold bars inside the bank vault somewhere on their thread, I clearly remember this because I was part of their bounty campaign. I think the previous project was Aurum, I don't know how it works but its also backed by gold.
What can you do with picture? Nothing. Once something happens they can just sell that gold or pick it up. There is nothing that can force them to hand that gold to token owners. Nothing. If there would be some storeroom with unbreakable lock that could be opened only with your token then could work. But like this is silly. You give them full trust. Sort of stupid if you can just buy gold yourself and put it under your pillow.