A transaction authorization system comprising a plurality of mobile devices each configured by a transaction authorization application, a central server, and an image capture device, having a feature extraction module, wherein:
- the central server is configured to maintain a set of user accounts, each associated with a corresponding one of the plurality of mobile devices, each user account comprising:
- a set of user-identifying features, including at least one of:
- an image of a user-identifying asset, and information that is derivable from an image of a user-identifying asset;
- location data, including the location of the associated mobile device, and a location update time for indicating when that location of the associated mobile device was updated;
- and
- transactional data for performing a transaction;
- the system is configured to execute a set of sequential operations for transaction authorization, comprising:
- (i) activating, at an appropriate time for sending a location update, a positioning module of one of the plurality of mobile devices to determine the current location of the mobile device;
- (ii) determining a location of the mobile device, via the positioning module;
- (iii) transmitting, by the mobile device, in response to step (i) and (ii), the determined location to the central server so as to update the location data of the user account with which that mobile device is associated;
- (iv) following transmission, placing the positioning module of the mobile device into a low-power sleep mode so as to conserve energy:
- (v) automatically capturing and transmitting, by the image capture device located at a service location, an image of a user-identifying asset;
- (vi) receiving, by the central server, after completion of step (v), the image from the image capture device, and features derived from the image from the image capture device,
- (vii) determining, by the central server, subsequent to steps (i)-(vi), a match with one of the user accounts dependent on:
- image similarity, including the similarity of features of the captured image, and those of the set of user-identifying features;
- and
- location similarity, including the similarity of the known location of the service location, and the location of the mobile device by:
- calculating a time difference between a time of capture of the image of the user-identifying asset, and the time of the mobile device location update;
- calculating a distance between the known location of the service location, and that of the mobile device location;
- determining the probability of the mobile device travelling the calculated distance within a period corresponding to the calculated time difference;
- and
- filtering out user accounts where the determined probability is below a predetermined value;
- and
- (viii) authorizing, by the central server, only upon determining a match in step (vii), use of the transactional data of the user account with which a match has been determined to perform a transaction, thereby to permit service provision at the service location within a predetermined timeframe from a capture time of the captured image used by the server to determine a match with that user account.