  Mobile payment systems are increasingly used to simplify the way in which
money transfers and transactions can be performed. We argue that, to achieve
their full potential as economic boosters in developing countries, mobile
payment systems need to rely on new metaphors suitable for the business models,
lifestyle, and technology availability conditions of the targeted communities.
The Pay-with-a-Group-Selfie (PGS) project, funded by the Melinda & Bill Gates
Foundation, has developed a micro-payment system that supports everyday small
transactions by extending the reach of, rather than substituting, existing
payment frameworks. PGS is based on a simple gesture and a readily
understandable metaphor. The gesture - taking a selfie - has become part of the
lifestyle of mobile phone users worldwide, including non-technology-savvy ones.
The metaphor likens computing two visual shares of the selfie to ripping a
banknote in two, a technique used for decades for delayed payment in cash-only
markets. PGS is designed to work with devices with limited computational power
and when connectivity is patchy or not always available. Thanks to visual
cryptography techniques PGS uses for computing the shares, the original selfie
can be recomposed simply by stacking the shares, preserving the analogy with
re-joining the two parts of the banknote.
