Despite the name, FaceCash identifies purchasers with a bar code, not their face. FaceCash's face identification is the equivalent of credit cards with your photo on them. The photo is just casual security and doesn't help for online purchases.
My university's cafeteria linked student id cards with a debit system. To ensure cafeteria cashiers checked the cards' photos, "secret shoppers" would occasionally try to buy lunch with a card featuring a portrait of a friendly golden retriever. :)
The photo that matters for FaceCash is the one that is downloaded from the server onto the POS. The one on the phone is just for show, and cashiers are instructed to basically ignore it. So if you're a thief, you can't just put a JPEG of your thief-face next to someone else's barcode. The correct owner's face will still show up on the register.
My university's cafeteria linked student id cards with a debit system. To ensure cafeteria cashiers checked the cards' photos, "secret shoppers" would occasionally try to buy lunch with a card featuring a portrait of a friendly golden retriever. :)