The app, which Mr. Baptiste created with the Network for the Elimination of Police Violence, an advocacy group based in Toronto, is meant to make recording the police easier and to make the footage less vulnerable to confiscation by the authorities. Once a user uploads a video, the group is notified, and its staff can review and, if necessary, alert the news media and authorities of any apparent wrongdoing by police.

Though it is only the latest in a string of cases in which amateur photography has been used to document officers’ use of force, the South Carolina shooting demonstrates the power of citizen-captured video in the most salient way. Michael T. Slager, the officer in the case, initially said that Walter L. Scott, a driver who had been stopped for a broken taillight, had taken his stun gun during a scuffle. The video, captured on a cellphone by a bystander, instead showed the officer shooting Mr. Scott eight times while he ran away. On Tuesday, Mr. Slager was charged with murder.

Cop Watch is one of a number of programs for smartphones aimed at helping citizens broadcast encounters with the police. In 2011, during the height of the Occupy Wall Street movement, Jason Van Anden, an artist and technologist, created “I’m Getting Arrested,” an app that could automatically send text messages to a list of prepopulated close contacts with the push of a button. Later, inspired by Mr. Van Anden’s app, the New York Civil Liberties Union developed the “Stop and Frisk Watch” app, a response to a line of policing tactics championed by then-mayor Michael Bloomberg’s administration.

The N.Y.C.L.U. app allows a bystander to record from an Android-based phone or iPhone by just pressing a button on the phone’s frame. The app can send a report of a police encounter directly to the group for evaluation.

“We, sadly, thought the technology would be equally useful for young men of color in New York City,” said Jennifer Carnig, the director of communications for the N.Y.C.L.U. “Of course, in New York City if you touch your pocket to get your phone during an encounter with the police, you can end up dead.”