For once I heartily agree with the ACLU. In many States it is illegal to photograph police -- leading to many abuses. Where cameras are allowed, much police misbehaviour has been caught. Libertarian Radley Balko gives some of the history of it. It's not only blacks that the police abuse
"St. Louis - Police who work the Fairground neighborhood will soon be under video surveillance by the people they serve, an activist group said Wednesday.
The American Civil Liberties Union of Eastern Missouri first announced in December 2005 its intention to outfit residents to record city officers.
The program, Project Vigilant, has spent one and a half years in development.
Officials with the local ACLU chapter have said that city officers often mistreat and target blacks and that it hopes cameras would deter police abuse and smooth out police-neighborhood relations.
Source
My only objection to the above is that it is tokenism. If the ACLU were serious about reining in rogue police, they would be campaigning to have legal bans on photographing police overturned in the many States where they apply. In the above case, they have chosen one State where it is legal to photograph police.