  The impact of citizen journalism raises important video integrity and
credibility issues. In this article, we introduce Vamos, the first user
transparent video "liveness" verification solution based on video motion, that
accommodates the full range of camera movements, and supports videos of
arbitrary length. Vamos uses the agreement between video motion and camera
movement to corroborate the video authenticity. Vamos can be integrated into
any mobile video capture application without requiring special user training.
We develop novel attacks that target liveness verification solutions. The
attacks leverage both fully automated algorithms and trained human experts. We
introduce the concept of video motion categories to annotate the camera and
user motion characteristics of arbitrary videos. We show that the performance
of Vamos depends on the video motion category. Even though Vamos uses motion as
a basis for verification, we observe a surprising and seemingly
counter-intuitive resilience against attacks performed on relatively
"stationary" video chunks, which turn out to contain hard-to-imitate
involuntary movements. We show that overall the accuracy of Vamos on the task
of verifying whole length videos exceeds 93\% against the new attacks.
