Patent ID: 8775807

Claim:
A non-transitory computer-readable medium storing instructions executable by one or more computers that, upon execution, cause the one or more computers to perform operations comprising: storing, at a client device, a credential identifier associated with a user identifier and a location; receiving, at the client device, a request to output a graphical representation of the credential in a manner that enables a credential authority to validate the graphical representation; responsive to receiving the request to output the graphical representation of the credential: obtaining, at the client device, a time measured by a timing device of the client device; generating, at the client device, the graphical representation of the credential based on the credential identifier and the time; outputting, to a display of the client device, the generated graphical representation in a manner that enables the credential authority to validate the credential by visual inspection of the generated graphical representation; obtaining a location of the client device; determining that the location of the client device is within a predefined distance of the location associated with the credential; responsive to determining that the location of the client device is within the predefined distance of the location associated with the credential, storing, in a memory of the client device, data indicating that the user has entered the location associated with the credential.