Speaking of Baltimore, I had scarce been living here a year when I got arrested for this very thing. There's a badly designed intersection in my neighborhood that has resulted in the deaths of too many, and I document them to protest to the city to put in turn signals. This particular wreck was very bloody and messy, and both my fiancée and myself were taking pictures of the scene. Immediately two fat cops came running over telling us we couldn't take pictures because it "makes our cameras evidence." We were told if we deleted them we might be "allowed" to leave. I told them they were full of it and that I knew my rights. There's no way taking pictures of a wreck on public property is illegal (and I didn't take any pictures of any dead people, just the wreckage, they were gone before I got there). I even explained the purpose of these photos. One cop said if I didn't delete them in front of her, she'd arrest me, confiscate my phone, break it, and then release me without charges. She did just that. I filed many complaints, talked to lawyers, but she didn't break the law so I'm told.
There were tons of news people there recording the scene. There was a large towering apartment building with people taking pictures up there, but I guess harassing two young 20 somethings enforcing fictional laws is less work for the Baltimore police.