1. A system comprising: a data processing apparatus; and a non-transitory computer storage medium encoded with a computer program, the computer program comprising instructions that when executed by the data processing apparatus cause the data processing apparatus to perform operations comprising: receiving a digital video comprising video data; processing the video data to detect features indicative of a first human face in the digital video; determining, from the video data, a first frame, in which the features indicative of the first human face are detected in the digital video; determining first timestamp data corresponding to the first frame; generating a first identifier corresponding to the first human face; generating a data set comprising the first identifier and the first timestamp data; determining that the first identifier corresponds to a first member of a social networking service; linking the first identifier with a profile corresponding to the first member of the social networking service; appending the data set to the video data to provide annotated video data; and providing an indicator that indicates a presence of the first human face in the digital video while the digital video is playing, wherein the indicator is an annotation associated with the first human face, the indicator includes the first identifier of the first human face, and selection of the indicator causes information about the profile corresponding to the first member of the social networking service to be displayed on a user device.