They would be done in the way that I personally do, or at least something similar. The private key is split using Shamir's Secret Sharing Scheme into several pi

They would be done in the way that I personally do, or at least something similar. The private key is split using Shamir's Secret Sharing Scheme into several pieces, which is then printed as a high-redundancy QR code and then hidden. The key only needs to be 256bit, so there's not a lot of data to hide.