A security system includes a software application running in a user's smartphone and a separately carried visual key that the user can image at will with the smartphone's camera. An effective visual key would typically comprise digital data encoded in a series of colored cells arranged in a colorgram. Such digital data is treated as a what-you-have security factor, and is concatenated with other security factors so users can authenticate themselves to websites, internet services, and even within the smartphone device itself or its applications. In one aspect, when users authenticate themselves to a server, the server returns a short-term supply of one-time-passwords or account numbers for use in secure access and financial transactions on other systems.