By Gina Cherelus

(Reuters) - Police forces in 50 U.S. cities are failing to protect the civil rights and privacy of residents due to the inadequacy of programs that govern how their officers use body-worn cameras, a report by a coalition of rights groups said on Tuesday.

Many U.S. cities have approved or expanded the use of body cameras since August 2014, when a white police officer fatally shot an unarmed black teenager in Ferguson, Missouri. That incident triggered protests and a national debate about police use of force, especially against minorities.

The study was conducted for The Leadership Conference of Civil and Human Rights coalition by Upturn, a Washington DC-based company that studies how technology affects social issues.

"Body cameras carry the promise of officer accountability, but accountability is far from automatic," Harlan Yu, principal of Upturn, said on a conference call with reporters.

The study focused on the nation's largest police departments that have body-worn camera programs, as well as programs that have received federal funding, and those in cities that have had high-profile incidents involving law enforcement officers.

It judged them against eight criteria, including whether each department publishes its body camera policy, to what degree officers are allowed discretion about when they turn on and off their cameras, and whether officers involved in incidents are prohibited from watching the footage before they write reports.

The study found that none of the departments it analyzed met all the criteria, and that the police departments in Ferguson and in Fresno, California, failed all of them. Nearly half did not make body camera footage easily accessible to the public. (Link to the report:

Three major departments with programs - Detroit, Michigan, Aurora, Colorado, and Pittsburg, Pennsylvania - have not made their body camera policies public, the study said.

"It has been and remains the goal of Chief Cameron McLay to reach the point where policies are public," a spokeswoman for the Pittsburgh Bureau of Police said. "The Bureau's body-worn camera protocols are incomplete due to state law."

Representatives of the police departments in Aurora, Detroit and Ferguson did not immediately respond to requests for comment.

The coalition released an initial report in November 2015 that studied body camera programs from 25 departments.

The group said some issues have improved since that report, noting several departments, including Chicago, Washington D.C. and Cincinnati now provide individuals who are recorded the opportunity to view the footage.

"Without carefully crafted policy safeguards, these devices could become instruments of injustice rather than tools of accountability," Wade Henderson, the coalition's president and chief executive officer, said in a statement.

(Reporting by Gina Cherelus; Editing by Daniel Wallis and Dan Grebler)