Yes, it is legal to photograph police activity.
Both media and citizens have a constitutional right to photograph and record police officers conducting police business in public places. Unfortunately, throughout the country, some camera-shy and aggressive police have stopped people from recording public police action, confiscated their photography equipment, and even arrested them. Such police responses to citizen photographers have been condemned as unconstitutional by courts and public advocacy groups.
One result of such opposition, for example, is last year’s issuance by the DC Police Department of an order acknowledging that people have a First Amendment right to photograph and record police officers acting in an official capacity in any public space, as long as the photography doesn’t interfere with police activity.