In one week, three videos surfaced showing New York City police officers whacking men with batons or, in one case, violently knocking a protester off his bicycle in Times Square. Two of the confrontations were caught by amateurs, and the footage from one was posted on YouTube. In each case, the video footage might determine who - civilians or police - will face charges. Law enforcement officials say the episodes provide yet another example of how the proliferation of cheap digital recording devices could change how situations are investigated and how police are held accountable. "Digital media can be very compelling and powerful evidence. It can even be overwhelming in the right circumstances," said Jeremy Saland, a former Manhattan prosecutor who works now as a private defense attorney.