If you look at the police as a single entity, it's easy to loose sight of the fact that they are people. Try to connect with them as individuals, recognize them as human, let them know your human too. Humor is your friend:
IMAGE LINK: http://www.flickr.com …/64514660@N02/6255794895/
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lthnmsrtkn
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So far I've had no issues with the police either photographing them or bad treatment, and have seen them be very courteous to journalists of both video and photography. I've seen them show significant restraint as well. That may just be the region I'm in, or isolated experience that isn't representative though.
I think it's worth trying to put yourself in their shoes, they have a job to do too. Sometimes a pretty dangerous job, with immense consequences for any mistakes.
On the other hand I think we should document what happens, try to keep everyone honest and accountable. If you look close, you'll probably see them taking video/photos of you, so make it a two way street.