From the paper: > [Pay with a Group Selfie (PGS)] is a mobile payment technique that leverages on face-to-face exchanges where pictures taken with mobile phone

From the paper: > [Pay with a Group Selfie (PGS)] is a mobile payment technique that leverages on face-to-face exchanges where pictures taken with mobile phones are used to embed all information (the parties’ identities, the exchanged goods/services, and the price) of a business transaction. The system relies on Visual Cryptography (VC) to generate two untamperable shares of the selfie showing the transaction. The buyer and the seller hold a share each, and the transaction can be checked simply by stacking the shares.