Device activation for a service using an outputted representation

In one embodiment, a method activates a first device for using a service. A second device receives, from a third device, a user identifier for a user and a unique identifier for the first device. The user identifier originates from the third device and the unique identifier originates from the first device in a representation outputted by the first device. The second device determines a user account for the service, the user account being associated with the user identifier for the user. The second device associates the unique identifier for the first device with the user account. Then, the second device communicates with the first device to activate the first device to use the service in response to receiving the user identifier and the unique identifier. The second device allows access to the service from an application running on the first device.